Selina Concise Physics Class 6 ICSE Solutions – Light

Selina Concise Physics Class 6 ICSE Solutions – Light

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 6 Physics. You can download the Selina Concise Physics ICSE Solutions for Class 6 with Free PDF download option. Selina Publishers Concise Physics for Class 6 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina Concise ICSE Solutions for Class 6 Physics Chapter 5 Light

  • Synposis
  • Light itself is not visible, but in the presence of light other objects become visible A.
  • Light is defined as the external physical cause that affects the eye to produce the sensation of vision.
  • Two types of sources of light are:
    (1) Natural sources such as sun, stars andjugnu.
    (2) Artificial sources such as fire, electric lamp, electric tube light, a burning candle, a kerosene lamps heated bodies, etc.
  • The bodies which themselves emit light are called luminous bodies. Examples: torch, electric lamps electric tube light, burning candle, kerosene lamp, sun, stars. Jugnu etc.
  • The bodies which do not emit light by their own, but they become visible because of the light falling on them from a luminous body, are called non-luminous bodies. Examples: moon, earth, table, book, chair etc.
  • A medium which allows the passage of light through it easily, is called a transparent medium. Examples: glass, air, water etc.
  • A medium which allows only a small amount oflight to pass through it, is called a translucent medium. Examples: ground glass, tracing paper etc.
  • A medium which does not allow anydight to pass tough it, is called an opaque medium. Examples: wood, metals etc.
  • Light travels in a straight line path. This is called the rectilinear propagation oflight.
  • The pin hole camera is a simple application of the rectilinear propa – gation oflight.
  • The image (or picture) formed in a pin hole camera is upside down (i.e. inverted). On increasing the distance of screen from the pin hole, the size of image increases.
  • The shadow of an opaque object is the dark patch obtained on the screen when that opaque object is placed in the path of light.
  • Shadow is formed because light travels in a straight line path.
  • The shadow is similar to the shape of the object.
  • The part of the shadow where no light reaches from the source is completely dark and is called the umbra.
  • The part of the shadow where light reaches from only a portion of the source is partially dark and is called the penumbra.
  • There is only umbra in the shadow of an opaque object due to a point source. The umbra is bigger in size than that of the obj ect. The umbra increases in size if the screen is moved away from the object.
  • The shadow of an object due to a light source smaller than the object contains an umbra surrounded by a penumbra. The umbra is bigger in size than that of the object. Both the umbra and penum¬bra increase in size as the screen is moved away from the source.
  • The shadow of an opaque object due to a light source bigger than the object contains an umbra (which is much smaller in size than the object) surrounded by a penumbra. The umbra diminishes while the penumbra increases in size if the screen is moved away from the object.
  • Lunar and solar eclipses are the examples of formation of shadows in nature.
  • A lunar eclipse is caused on a certain full moon night when the earth comes in between the sun and the moon so that the earth casts its shadow on the moon.
  • A solar eclipse is caused on a certain new moon’s day when the moon comes in between the sun and the earth so that the moon casts its shadow

Test yourself

A. Short Answer Questions

1. Write true or false for each statement

(a) The moon is a natural source of light.
Answer. False

(b) The moon is self luminous.
Answer. False

(c) We can see an object through an opaque medium.
Answer. False

(d) Light passes through glass.
Answer. True

(e) Light travels in a straight line path. .
Answer. True

(f) Image formed in a pin hole camera is real.
Answer. True

(g) The image in a pin hole camera gets blurred if the hole is made bigger.
Answer. True

(h) A shadow is formed because light travels in a straight line path.
Answer. True

(i) Solar eclipse occurs when the sun comes in between the earth and the moon.
Answer. False

(j) If the shadow of earth falls on the moon, the eclipse is called the lunar eclipse.
Answer. True

2. Fill in the blanks

(a) Light gives us the sensation of vision.
(b) The sun is a natural source of light.
(c) A medium through which light cannot pass is called the opaque medium.
(d) A medium which allows light to pass through it easily is called the transparent medium.
(e) Moon is a non-luminous body.
(f) Light travels in a straight line path.
(g) In a pin hole camera, the image formed is inverted and real.
(h) The darkest portion of a shadow is called the umbra.
(i) The less dark portion of a shadow is called the penumbra.
(j) Lunar eclipse occurs when the earth comes in between the moon and the sun.

3. Match the following columns
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 1
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 2

4. Select the correct alternative

(i) The natural source of light is

  1. candle flame
  2. electric lamp
  3. sun
  4. kerosene lamp

(ii) The formation of inverted image in a pin hole camera shows that

  1. light enables us to see
  2. light travels in a straight line path
  3. light can pass through the pin hole
  4. light does not pass through the pin hole

(iii) The luminous body is

  1. a lighted bulb
  2. earth
  3. noon
  4. table

(iv) Umbra is a region of

  1. complete darkness
  2. partial darkness
  3. complete brightness
  4. partial brightness

(v) Penumbra is a region of

  1. complete darkness
  2. complete brightness
  3. partial brightness
  4. none of the above

(vi) Solar eclipse occurs on

  1. every new moon’s day
  2. certain new moon’s day
  3. every full moon’s day
  4. certain full moon’s day

(vii) Lunar eclipse occurs on

  1. every full moon’s night
  2. certain full moon’s night
  3. every new moon’s day
  4. certain new moon’s day

B. Short/Long Answer Questions

Question 1.
What is light ? Define it.
Answer:
Light is a form of Energy i. e. The external physical cause that affects our eye to produce the sensation of vision.

Question 2.
How does light make an object visible ?
Answer:
An object becomes visible to us when the light after striking the object reaches our eyes. Light itself is not visible, but light makes objects visible to us.

Question 3.
Name two natural sources of light.
Answer:
Sun, stars,jugnu, firefly.

Question 4.
List two artificial sources of light.
Answer:
Electric bulb, torch, an oil lamp, fluorescent tube, candle.

Question 5.
Differentiate between the luminous and non-luminous bodies. Give two examples of each.
Answer:
Difference Between
Luminous
The bodies which have light of their own e.g. sun stars, bulb, candle, oil lamp, torch, a lantern.
Non-Luminous
The bodies-which do not have their own Iight.e.g. moon, chair, table. When light falls on them, they become visible.

Question 6.
Is the moon a luminous object ?
Answer:
Moon is not a luminous body, it is nbn-luminous body. It has no light of its own.

Question 7.
What do we call a body that shmes on its own ?
Answer:
The bodies that shines onits ownor whichthemselves emittheir own light are called the luminous bodies.

Question 8.
What do we call an electric bulb producing light ?
Answer:
Luminous object.

Question 9.
What is a transparent medium ? Give two examples.
Answer:
Amedium which allows the passage of light through it easily,is called a transparent medium.
Examples: glass, air, water etc.

Question 10.
Explain the difference between a transparent, a translucent and an opaque medium. Give two examples of each.
Answer:

  1. Transparent objects — Those objects through which light can pass easily are called transparent obj ects. e.g. Water, glass, air.
  2. Translucent object— The ohj ect through which light can pass partially are called translucent object, e.g. tracing paper, waxed paper.
  3. Opaque object— The objects which do not allow the light to pass through are called opaque objects, e.g. wood.

Question 11.
What do we call a substance through which we cannot see light ? Give an example of such a substance.
Answer:
A substance through which we cannot see light is called an opaque medium.
Examples:  Wood, metals, butter paper and black paper etc.

Question 12.
What do we call a substance through which light passes ? Give an example of such a substance.
Answer:
A substance through which light passes is called a transparent substance.
Examples: glass, air, water etc.

Question 13.
Can a transparent medium form an image ? Explain your answer.
Answer:
No, a transparent medium cannot form image. All the light that passes through a transparent medium completely pass through the substance. For the formation of image it is must that the light rays get reflected through the surface.

Question 14.
How can you obtain a point source of light ?
Answer:
A point source of light is obtained either by placing a screen having a fine hole, in front of die luminous body or by placing the luminous body inside a box having a fine hole on one of its side.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 3

Question 15.
Define the terms : a ray of light and a beam of light.
Answer:
The light travelling in any one direction in a straight line is called a ray of light.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 4
A group of light rays given out from a source is called a beam of light
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 5

Question 16.
What do you mean by ‘rectilinear propagation of light’ ?
Answer:
Light travels in a straight line path. This is called the rectilinear propagation of light.

Question 17.
Describe an experiment to show that light travels in a straight line path.
Answer:
Take three cardboards A, B and C each about 25 cm square. Take a pin and make a small hole in each cardboard at the same height. Suspend the cardboard pieces by separate threads vertically from a support such that each hole is at the same height, as shown. Pass a string through the holes and pull it taut. This makes the three holes in a straight line. Now take out the string.
Place a lighted candle near one of the cardboards (say A). Look at the candle flame from the other side of the cardboard C. The candle flame is clearly seen.
Now slightly displace one of the cardboards (say B) so that the holes no longer remain in a straight line. Again look at the candle flame from the other side of the cardboard C. You do not see the candle flame. The reason is that light travels in a straight line and now the holes in the cardboards A, B and C are not in a straight line.
Conclusion: Light travels in a straight line path called the rectilinear propagation of light.

Question 18.
In which of the following two arrangements (a) and (b) shown in the diagram, you can see the light of the bulb ? Explain Your answer
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 6
Answer:
We can see the light of the bulb in the arrangement (a).
This is so because in arrangement ‘a’ the rod is straight and light travels in a straight line path.
Whereas in arrangement ‘b’ the rod is bent. So the light cannot pass through it.

Question 19.
Name a simple application of the rectilinear propagation of light
Answer:
The simple applications of rectilinear propagation of light are pin hole camera, formation of shadows and elipses.

Question 20.
What is a pin hole camera ? Draw a neat and labelled diagram to show the formation of image of a lighted candle by it.
Answer:
The pin hole camera is a simple application of the rectilinear propagation of light.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 7

Question 21.
Explain the formation of image of a luminous object in a pin hole camera with the aid of a neat diagram.
Answer:
When a luminous object AB, such as a lighted candle, is placed in front of the pin hole, an inverted picture A’ B’ of the candle is
obtained on the tracing paper. This picture A’ B’ is called the image. The image obtained is upside down (i. e. inverted). The reason is that the light travels in a straight line path. Hence light from the upper point A of the candle passes through the pin hole and strikes
the tracing paper at A’. Similarly, light from the lower point B of the candle passes through the pin hole and strikes the tracing paper
(or screen) at B’. Light from all the other points between A and B, on passing through the pin hole strikes the tracing paper in between
A’ and B’. As a result, an inverted image of the candle is seen on the tracing paper Fig shows the simple ray diagram for die formation of image.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 8

Question 22.
State two factors which affect the size of image formed in a pin hole camera.
Answer:
Factors affecting the size of the image :
The size of image depends on the following two factors:

  1. The distance of screen (i.e. tracing paper) from the pin hole, and
  2. The distance of obj ect (i.e. candle) in front of the pin hole.

Question 23.
Is the image obtained in a pin hole camera erect or inverted ? Give reason for your answer.
Answer:
Image obtained in a pin hole camera is inverted.
The reason is that the light travels in a straight line path. Hence light from the upper point of the candle passes through the pin hole and strikes the tracing paper in the lower point. Similarly light from the lower point of the candle passes through the pin hole and strikes the tracing paper at the upper point.

Question 24.
How is the image affected in a pin hole camera when another fine hole is made near the first pin hole ?
Answer:
If another pin hole is made near the first pin hole, two images are formed on the screen, one due to each of the two pin holes. If the holes are very close, the two images tend to overlap each other. As a result, a blurred image will be seen.

Question 25.
State the effect on the image in a pin hole camera if

  1. The hole is made bigger.
  2. The luminous object is moved towards the pin hole.
  3. The length of the pin hole camera is increased (le. the screen is moved away from the pin hole).

Answer:

  1. If the hole is bigger than a pin hole, again a blurred image in seen. The reason is that a bigger hole is equivalent to a large number of pinholes. Each pin hole produces one image. These images overlap each other resulting in a blurred image.
  2. If the object is moved towards the pin hole the size of the image increases.
    The size of image / The size of object = Distance of screen from pin hole / Distance of object from pin hole
  3. When the length of the pin hole camera is increased. C is the screen is moved away from the pinhole, the size of image also increases.

Question 26.
What is a shadow ? Give a reason for its formation.
Answer:
Shadow : When light falls on an opaque object, light is obstructed and a dark patch on a screen kept behind is called shadow. This is because light propagates in straight line. If distance between obj ect and screen is less, the shad o w will be (umbra) dark and smaller.
If the distance is increased shadow will be dim and larger.

Question 27.
Draw a ray diagram to show the formation of shadow of an opaque object by a point source of light. How is the size of shadow affected if the screen is moved away from the object?
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 9
If we move the screen away from the object, the shadow increases in size.

Question 28.
State two differences between an umbra and a penumbra.
Answer:
Umbra

  1. It is the portion of shadow where no light reaches from the source of light due to the opaque object.
  2. It is completely dark.

Penumbra
It is the portion of shadow where a portion of light from the source of light reaches the shadow even in the presence of the opaque object in between them.
It is not completely dark, but is dim (or less bright).

Question 29.
Draw a ray diagram to show the formation of umbra alone.
Answer:
Formation of umbra alone.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 10

Question 30.
Draw a ray diagram to show the formation of umbra and penumbra both. Label the parts umbra and penumbra in your diagram.
Answer:
If your move the screen away from the object, the shadow increases in size. Formation of umbra and penumbra both.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 11

Question 31.
In each of the following diagrams, draw rays to form umbra and penumbra on the screen.
(a)

Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 12
(b)

Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 13
Answer:
(a)A’B’—umbra
Umbra alone is obtained on the screen when the opaque object is illuminated by a point source of light.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 14
(b)
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 15
EF is Penumbra CD is umbra.

Question 32.
State the conditions when only the penumbra of an opaque object is obtained on the screen.
Answer:
If the size of source of light is bigger than the size of the opaque object, the size of umbra is very small. If the screen is moved away from the object, the umbra vanishes and only the penumbra remains.

Question 33.
Why is it that the birds flying in the sky do not cast their shadow on the earth ?
Answer:
We do not see the shadow of a bird flying high up in air because in their shadow, the umbra is absent and the penumbra is too large and too faint that it is not visible as the distance of screen (i.e. earth) is very large from the object (i.e. bird).

Question 34.
Why are shadows at noon shorter than in the morning or in the evening ?
Answer:
At noon the sun is directly overhead. So, the sun rays fall vertically on the body. Hence the shadow is very short. In the morning and evenings, the sun rays fall in an inclined position. So, the shadows are long.

Question 35.
What is an eclipse ? Name the two types of eclipses.
Answer:
Eclipses are the examples of formation of shadows in nature. There are two kinds of eclipses:

  1. Lunar eclipse (the eclipse of the moon), and
  2. Solar eclipse (the eclipse of the sun).
    Lunar eclipse is due to the formation of shadow of earth on moon and solar eclipse is due to the formation of shadow of moon on earth.

Question 36.
When does a lunar eclipse take place ? Does it occur on every full moon’s night ?
Answer:
A lunar eclipse occurs when the earth comes in between the sun and moon and casts its shadow on moon. On a full moon night, the moon rises in the east after sun sets in the west. On such a night, the sun and moon are on the opposite sides of the earth. The shadow of the earth falls on the surface of the moon therefore moon is not visible to us. This is lunar eclipse as shown in the figure.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 16

Question 37.
Draw a diagram to show the formation of lunar eclipse.
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 17

Question 38.
When does a solar eclipse take place ? Does it occur on even’ new moon’s day ?
Answer:
Solar eclipse— On a certain moon’s day the moon, happens to come in between the sun and the earth. They come in a straight line. In such a situation, the moon being smaller in size casts its shadow only on a limited region on the earth. In these regions of the earth, the solar eclipse occurs.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 18

Question 39.
Draw a diagram to show the formation of solar eclipse.
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 19

Question 40.
What is annular solar eclipse ? Draw a labelled diagram to show its formation.
Answer:
An annular solar eclipse occurs when only the tip of the umbra of the moon falls on the earth. From the point D, the sun will appear to be completely obstructed by the moon, only the outer rim of the sun, called corona, is then visible for a very short time which is known as the diamond ring. The formati on of annular solar eclipse is shown below.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 20

Selina Concise Physics Class 6 ICSE Solutions – Force

Selina Concise Physics Class 6 ICSE Solutions – Force

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 6 Physics. You can download the Selina Concise Physics ICSE Solutions for Class 6 with Free PDF download option. Selina Publishers Concise Physics for Class 6 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina Concise ICSE Solutions for Class 6 Physics Chapter 3 Force

  • Synposis
  • A body not changing position with time with respect to a nearby fixed object is said to be at rest.
  • A body changing position with time with respect to a nearby fixed object is said to be in motion.
  •  Force is a push or pull which can change the state of rest or motion of the body or can change the size and shape of the body (i.e. it can deform a body).
  • A force applied on a body can
    (a) move it, if it is not in motion
    (b) stop it, if it is moving
    (c) increase or decrease its speed
    (d) change its direction of motion
    (e) change its shape or size if it is not free to move.
  • Force is defined as that cause which changes the state of rest or the state of motion of a body and can also deform it.
  • A force has both the magnitude and the direction.
  • When two forces act in opposite directions, the net force is equal to the difference of these forces, in the direction of the bigger force.
  • When two forces act on a body which are equal in magnitude but opposite in direction, the net force on the body is zero.
  • Forces are of two types :
    1. contact forces and
    2. non-contact forces (or forces at a distance).
  • Contact forces are
    1. the muscular force applied as push or pull,
    2. force of friction
    3. the force of reaction normal to the surface and
    4. the force of tension in a string pulled by a load.
  • Non-contact forces are
    1. gravitational force
    2. electrostatic force and
    3. magnetic force
  • The weight of a body is the force with which the earth pulls the body.
  • The unit of weight (or force) is kgf not kg which is unit of mass.
  • Friction is a force that opposes the motion.
  • Friction always acts in a direction opposite to the direction of motion.
  • The cause of friction is the interlocking of the irregular projections on the two surfaces in contact. ‘
  • The force of friction depends on:
    (a) the smoothness (or roughness) of the surfaces in contact, and
    (b) the weight of the sliding (or rolling) body.
  • The force of friction does not depend on the area of the surfaces in contact.
  • The disadvantages of friction are :
    (a) Friction opposes the motion
    (b) Friction produces heat
    (c) Friction causes wear and tear
    (d) Friction reduces efficiency
  • Friction can be reduced by
    (a) making the surfaces smooth
    (b) the use of lubricants
    (c) the use of ball bearings
    (d) streamlining the shape of the moving body.
  • The maximum force exerted by a surface on a body so long as it remains stationary is called the force of static friction.
  • The minimum force required to keep the body moving over a surface such that it moves equal distances in equal intervals of time is called the force of sliding friction.
  • The minimum force required to roll a body on a surface is called the force of rolling friction.
  • Rolling friction is less than the sliding friction and sliding friction is less than the static friction.
  • Friction is advantageous to us in almost all activities of our life.

Test yourself

A. Objective Questions

1. Write true or false for each statement

(a) The frictional force acts in the direction of motion of body
Answer. False

(b) The unit of weight is kilogram
Answer. False

(c) A force can change the direction of motion of a moving body.
Answer. True

(d) A force increases the mass of the body when applied on it.
Answer. False

(e) The force of friction is always disadvantageous.
Answer. False

(f) The sliding friction is more than the rolling friction.
Answer. True

(g) Liquids offer more friction than the gases.
Answer. True

(h) A wet oily road offers more friction than a dry rough road.
Answer. False

2. Fill in the blanks

(a) Force is applied as push or pull.
(b) On squeezing a gum tube, its shape changes.
(c) On pulling a string, its length increases.
(d) A moving football when kicked, its direction of motion changes.
(e) On applying brakes on a moving car, its speed slows down.
(f) We use ball bearings to reduce the friction.
(g) Friction opposes the motion.
(h) Lubricants are used to reduce friction.
(i) Friction causes wear and tear of moving parts of machine.

3. Match the following columns

Selina Concise Physics Class 6 ICSE Solutions Chapter 3 Force 1

Answer.

Selina Concise Physics Class 6 ICSE Solutions Chapter 3 Force 2

4. Select the correct alternative 
(a) A body falls downwards because of

  1. electrical force
  2. gravitational force
  3. mechanical force
  4. magnetic force.

(b) A force does not change

  1. mass
  2. length
  3. shape
  4. state of motion.

(c) A force to be expressed correctly requires

  1. only the magnitude
  2. only the direction
  3. both the magnitude and direction
  4. none of the above.

(d) Friction

  1. promotes motion
  2. opposes motion
  3. acts in the direction of motion
  4. is always a nuisance.

(e) Friction is reduced by

  1. making the surfaces wet
  2. making the surfaces dry
  3. making the surfaces rough
  4. sprinkling sand on the surface.

(f) Friction

  1. causes wear and tear
  2. produces heat
  3. stops a moving body
  4. has all the above disadvantages

(g) Friction is increased if

  1. an oil is sprayed
  2. the surfaces are made wet
  3. the surfaces are made dry
  4. the surfaces are polished

B. Short/Long Answer Questions

Question 1.
Name the term used for the push or pull ?
Answer:
Force

Question 2.
Give one example each of a force as

  1. a push
  2. as pull
  3. a stretch and
  4. a squeeze.

Answer:

  1. a push — To1 open a door, we push it.
  2. as pull — To move a grass roller on a lawn, it is pulled by a gardener.
  3. a stretch — Stretching a rubber string.
  4. a squeeze —Change in shape of a sponge on squeezing.

Question 3.
Explain the meaning of the term force.
Answer:
Force: Force is a physical cause that changes or may tend to change the state of rest or the state of motion of an object. The S.I. unit of force is Newton.

Question 4.
What effect can a force have on a stationary body ?
Answer:
When a force is applied on a stationary body, it begins to move.

Question 5.
What effects can a force have on a moving body ?
Answer:
When a force is applied on a moving body, it can be made to stop or it can change the direction of motion.

Question 6.
What effect can a force produce on a body which is not allowed to move ?
Answer:
When a force is applied on a body which is not free to move, it gets deformed i. e., the shape or size of the body changes.

Question 7.
Give one example each to indicate that the application of a force

  1. produces motion
  2. stops motion
  3. slows down motion
  4. changes the direction of motion
  5. deforms a body

Answer:

  1. A car originally at rest when pushed, begins to move.
  2. A moving bicycle is stopped by applying the brakes.
  3. The speed of a moving vehicle is slowed down by applying the brakes.
  4. A player kicks a moving football to change its direction of motion.
  5. On stretching a rubber string, its length increases.

Question 8.
State the effect produced by a force in the following cases :
(a) The sling of a rubber catapult is stretched
(b) A man pushes a heavy cart
(c) A player uses his stick to deflect the ball .
(d) A cyclist applies brakes
(e) A spring is compressed.
Answer:
(a) The shape and size of catapult changes i.e., its length increases.
(b) The heavy cart begins to move.
(c) The direction of the ball changes.
(d) The speed of the moving cycle is slowed down.
(e) There is change in size and shape of spring.

Question 9.
Name the two kinds of forces in nature.
Answer:
Two kinds of forces in nature are :

  1. Contact forces
  2. Non contact forces

Question 10.
Name the type of force which acts in the following cases:
Answer:
(a) A coolie lifts a luggage
Answer. Muscular force
(b) A bicycle comes to rest slowly when the cyclist stops pedalling
Answer. Frictional force
(c) A stone falls from a roof
Answer. Gravitational force.
(d) A comb rubbed with silk attracts the bits of paper
Answer. Electrostatic force
(e) A string hangs with a load
Answer. Force of tension.
(f) A horse moves a cart
Answer. Muscular force
(g) A magnet attracts an iron pin
Answer. Magnetic force
(h) A boy opens the door
Answer. Muscular force
(i) An apple falls from a tree
Answer.Gravitational force
(j) A man rows a boat.
Answer. Muscular force.

Question 11.
What do you mean by the gravitational force ? Give an example to illustrate it.
Answer:
The force of attraction on a body by earth is called gravitational force.
Example : The leaves and fruits fall from a tree downwards towards the ground, water in a river flows down streams, a ball thrown up goes to a height and then returns back on ground are some examples of motion due to gravitational force.

Question 12.
Define the term “weight of a body”
Answer:
Weight: The weight of the body is the force with which the earth attracts it towards the centre. It depends on acceleration due to gravity.

Question 13.
What do you understand by the term friction ?
Answer:
Friction: Friction is that force which opposes the relative motion between the two surfaces that are in contact with each other.

Question 14.
Give an example to illustrate the existence of force of friction.
Answer:
If we stop paddling our bicycle, it gradually slows down and ultimately it stops after travelling a certain distance. This is due to frictional force between bicycle and ground.

Question 15.
What is the cause of friction ?
Answer:
The cause of friction is the interlocking of the irregular projections on the two surfaces in contact.

Question 16.
State two factors which directly affect the force of friction.
Answer:
Two factors which directly affect the force of friction are :

  1. The smoothness of the surface.
  2. The presence of solid, liquid or gas around the moving body.

Question 17.
In which case will there be more friction between the truck and the road : when the truck is empty or when it is loaded ?
Answer:
When the truck is loaded there will be more friction between the truck and the road.

Question 18.
Which offers more friction on a body : a glass surface or a wooden surface ?
Answer:
Wooden surface offers move friction on a body.

Question 19.
Name the three kinds of friction.
Answer:
Friction is of three kinds :

  1. Static friction
  2. Sliding friction,
  3. Rolling friction

Question 20.
List three disadvantages of friction.
Answer:
Disadvantages of friction:

  1. Friction produces heat which damages the moving parts of a machine.
  2. Friction produces wear and tear on the contacting surfaces. This reduces the life of machine parts, tyres and shoe soles.
  3. A lot of energy is wasted due to friction to overcome it before moving.

Question 21.
When you apply the brakes, the bicycle stops and the rim of the wheel becomes hot. Explain the reason.
Answer:
It is due to friction between the brakes and the rim of the wheel that it becomes hot.

Question 22.
The eraser gets smaller and smaller as you use it more and more. Explain the reason.
Answer:
The eraser gets smaller and smaller as we use it more and more due to frictional force causing wear and tear of the eraser.

Question 23.
List three ways of reducing friction.
Answer:
Ways to reduce friction:

  1. Providing ball bearings or wheels between the moving parts of machine or vehicles reduce friction and allow smooth movement as rolling friction is less than sliding friction.
  2. Oiling or lubricating (with graphite or grease) the moving parts of a machine reduces friction. Fine powder like talcum powder also works as a lubricant to reduce friction.
  3. Polishing the rough surface reduces friction offered by it.
  4. Streamlining (giving special shape to experience minimum drag) the bodies of aeroplanes, cars, boats and ships help reduce drag (fluid friction) while travelling through air or water.

Question 24.
It is difficult to open an inkpot with greasy or oily hands. Explain.
Answer:
When the hands are oily, then the oil acts as lubricant and reduces the friction.
As the friction force is less, it is difficult to get grip of the inkpot and it becomes difficult to open it.

Question 25.
It is difficult to walk on a wet road. Explain.
Answer:
When the road becomes wet after rain, friction is reduced and hence, the road becomes slippery.

Question 26.
Give three examples to illustrate that friction is a necessary evil.
Answer:
The examples to illustrate that friction is a necessary evil are:

  1. If friction were absent, we would not be able to walk.
  2. Friction is necessary to burn a matchstick.
  3. It is due to friction that we can write on a board by a chalk.

Question 27.
Define

  1. static friction
  2. sliding friction and
  3. rolling friction

Answer:

  1. The maximum force exerted by a surface on a body so long as it remains stationary is called the force of static friction.
  2. The minimum force required to keep the body moving over a surface such that it moves equal distances in equal intervals of time is called the force of sliding friction..
  3. The minimum force required to roll a body on a surface is called the force of rolling friction.

Question 28.
Arrange the following in descending order :

  1. static friction
  2. sliding friction and
  3. rolling friction?

Answer:
Static friction > Sliding friction > Rolling friction.

Question 29.
A body needs a force F1 just to start motion on a surface, a force F2 to continue its motion and a force F3 to roll on the surface. What is

  1. the static friction
  2. sliding friction and
  3. rolling friction ? State whether F2 is equal, less than or greater than (1) F1 and (2) F3.

Answer:

  1. F1 = Static friction
  2. F2 = Sliding friction
  3. F3 = Rolling friction
    F1 > F2 > F3
    F2 is less than F1 but greater than F3.

Selina Concise Physics Class 6 ICSE Solutions – Simple Machines

Selina Concise Physics Class 6 ICSE Solutions – Simple Machines

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 6 Physics. You can download the Selina Concise Physics ICSE Solutions for Class 6 with Free PDF download option. Selina Publishers Concise Physics for Class 6 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina Concise ICSE Solutions for Class 6 Physics Chapter 4 Simple Machines

  • Synposis
  • Work is said to be done when a force applied on a body moves it. If the body does not move on applying a force on it, no work is done by the force.
  • The capacity of doing work is called energy.
  • A machine is a device which helps us to do work more easily.
  • A machine enables us to apply a less effort for a load greater than the effort or to apply the effort at convenient point and in a desired direction.
  • Some machines are simple and some are complex.
  • The mechanical advantage of a machine is the ratio of the load to the effort, i.e., Mechanical advantage = Load / Effort
  • Smaller the effort required for a certain load, greater is the mechanical advantage of the machine.
  • The efficiency of a machine is the ratio of the useful work done on the load by the machine to the work put into the machine by the effort, i.e.
    Efficiency = Work output / Work input
  • The efficiency of an ideal machine is 1 (or 100 per cent).
  • The efficiency of an actual machine is less than 1 because some part of the work put into the machine is lost in overcoming the friction between the moving parts of the machine.
  • A lever is a simple machine which we most commonly use in our daily life. It is a rod which can turn about a fixed point called the fulcrum.
  • The mechanical advantage of a lever is equal to the ratio of the effort arm to the load arm, i.e. Mechanical advantage of a lever = Effort arm / Load arm
    The levers are of three kinds :
    Class I levers which have fulcrum in between the load and the effort.
    Class II levers which have load in between fulcrum and the effort.
    Class III levers which have effort in between the fulcrum and the load.
  • The mechanical advantage of class I lever can be 1, more than 1 or less than 1.
  • The mechanical advantage of class II levers is always more than 1.
  • The mechanical advantage of class III levers is always less than 1.
  • A pulley is a simple machine which is used for raising a load up by applying the effort downwards.
  • The mechanical advantage of an ideal pulley is 1. In an actual pulley, due to friction, the mechanical advantage is less than 1 (i.e., the effort is more than the load).
  • The pulley allow us to apply the effort downwards which is a convenient direction.
  • The wheel and axle is a simple machine having a wheel and an axle. The linear motion of axle is obtained by rotating the wheel so as to reduce friction. Example: Steering wheel, screw drivers, water tap etc.
  • An inclined plane is a simple machine which is used to move a load up with a less effort. It is a sloping (or slanting) surface.
  • Less the slope of the inclined plane, less is the effort needed to push a load up.
  • The mechanical advantage of an inclined plane is greater than 1 (i. e. a less effort is required to push a heavy load up an inclined plane).
  • A wedge is a sharp edge formed by joining the two inclined planes together. Example: nail, knife, axe, plough etc.
  • A screw is a modified form of an inclined plane.
  • A screwjack is a simple machine having a combination of a screw and a lever. It is used to lift the heavy vehicles such as cars, trucks, buses etc.
  • Machines are used for our convenience. Therefore, we should take proper care of a machine by painting the machine parts to avoid rusting, lubricating its parts to reduce friction etc. This increases the life span of the machine.

Test yourself

A. Objective Questions

1. State whether the following statements are True or False.

(a) A boy does work while pushing a wall.
Answer. False

(b) A machine performs work by itself.
Answer. False

(c) In an ideal machine, work done on load is equal to the work done by effort.
Answer. True

(d) All levers are force multipliers.
Answer. False

(e) A pulley changes the direction of force.
Answer. True

(f) An inclined plane always has the mechanical advantage more than 1.
Answer. True

2. Fill in the blanks

(a) The useful work done by an actual machine is always less than the work done on the machine.
(b) In class II levers, the load is in between fulcrum and effort.
(c) The mechanical advantage of class III lever is always less than 1.
(d) A pulley is used to change the direction of effort.
(e) Mechanical advantage of an inclined plane is always greater than 1.

3. Match the following

Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 1

Answer.

Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 2
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 3

4. Select the correct alternatives

(a) For an ideal machine, the efficiency is

  1. greater than unity
  2. less than unity
  3. equal to unity
  4. depends on the value of load

(b) Mechanical advantage of a machine is defined as:

  1. Load X Effort
  2. Load / Effort
  3. Load + Effort
  4. Effort / Load

(c) The mechanical advantage of a lever is equal to:

  1. Load arm / Effort arm
  2. Effort arm / Load arm
  3. Load arm + Effort arm
  4. Load arn — Effort arm

(d) A pulley is used because it

  1. has the mechanical advantage greater than one
  2. has 100% efficiency
  3. helps to apply the force in a convenient direction
  4. requires more effort to raise a less load.

(e) Wheel is used with axle because

  1. sliding friction is less than the rolling friction
  2. rolling friction is less than the sliding friction
  3. they work as the inclined plane
  4. They help us to change the direction of force.

B. Short/Long Answer Questions

Question 1.
When is work said to be done by a force ?
Answer:
Work is said to be done when a force moves an obj ect through a distance in its own direction.

Question 2.
What is energy ?
Answer:
Energy: The ability or capacity to do work is called energy.

Question 3.
What do you understand by a machine ?
Answer:
Machine: A machine is a device that allows us to do work with less effort. Machines make our work easier to do. Machines have made our li ves comfortable and faster.

Question 4.
What is the principle on which a machine works ?
Answer:
Principle of a Machine: The work output of a machine is equal to the work input.

Question 5.
State two functions of a machine.
Answer:
Various functions that a machine can perform are:

  1. Changing the direction of applied force — Example: When a flag is hoisted with the help of a pulley.
  2. Changing the magnitude of applied force — Example: Bottle opener multiplies the applied force and much less effort is required to open the cap.
  3. Applying force at a convenient point — Example: In a pair of scissors, the input force is applied at the handle of the scissors which cuts the paper at the other end of the blade.
  4. Changing the speed of an object — Example: While riding a bicycle, force is applied on pedals which multiplies the speed.

Question 6.
Name six simple machines. Give an example of each machine.
Answer:
The Simple Machines and there examples are as follows:

  1. The lever: Examples are a crow bar, claw hammer, a pair of pilers etc.
  2. The Inclined plane: Examples are ramp, staircase, hilly roads etc.
  3. The wedge: Examples are knife, axe, plough, nail etc.
  4. Screw: Examples are A screw.
  5. The wheel and axle: Examples are steering wheel of a car, bicycle pedal etc.
  6. The pulley: Examples are a pulley used in raising a load.

Question 7.
Define the term ‘work input’ and ‘work output’ in relation to a machine.
Answer:
Work input is work done on a machine equal to the effort force times the distance through which the force is applied.
Work output is work that is done by a machine equals resistance force times the distance through which the force applied.
For an ideal machine, the work output is equal to the work input i. e. the efficiency.

Question 8.
Explain the term mechanical advantage of a machine.
Answer:
The mechanical advantage of a machine is the ratio of the load to the effort. In other words
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 4

Question 9.
Define the term efficiency of a machine.
Answer:
The ratio of the work done by the machine to the work done on the machine is called efficiency of a machine
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 5
(Work done by a machine is called the output energy and the work done on a machine is called the input energy.)

Question 10.
What is an ideal machine ?
Answer:
A machine is which no part of the work done on the machine is wasted, is called an ideal or perfect machine. Thus, for an ideal machine, the work output is equal to the work input, i.e., the efficiency of an ideal machine is 1 (or 100 per cent).

Question 11.
Can a machine have an efficiency of 100% ? Give a reason to support your answer.
Answer:
Efficiency of a machine is always less than 100% as output energy is always less than the input energy, because some energy is lost to overcome friction.

Question 12.
A machine is 75% efficient’. What do you understand by this statement ?
Answer:
If a machine is 75% efficient, it means that 75% of the work input to the machine is obtained as the useful work output. The remaining 25% of the work input has been lost in overcoming the friction.

Question 13.
What is a lever ?
Answer:
Lever: A lever is a simple rigid bar which is free to move around a point called fulcrum.

Question 14.
Describe three orders of levers giving an example of each. Draw neat diagrams showing the positions of fulcrum, load and effort in each kind of lever.
Answer:
The levers are of three kinds :
Class I levers which have fulcrum in between the load and the effort.
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 6
Class II levers which have load in between the fulcrum and the effort.
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 7
Class III levers which has effort in between the fulcrum and the Load
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 8

Question 15.
What do you mean by the mechanical advantage of a lever ?
Answer:
The mechanical advantage of a lever is equal to the ratio of the effort arm to the load arm. This is also called the principle of a lever.

Question 16.
Which class of lever has the mechanical advantage always more than 1 ? Give an example.
Answer:
The mechanical advantage of class II levers is always more- than 1.
Example – Nut cracker, wheel barrow, bottle opener etc.

Question 17.
Which class of lever has the mechanical advantage always less than 1 ? Give an example.
Answer:
The mechanical advantage of class III levers is always less than 1.
Example: a pair of tongs, sugar tongs, knife, forceps etc.

Question 18.
Give one example of class I lever in each case where the mechanical advantage is

  1. more than 1
  2. equal to 1
  3. less than 1.

Answer:

  1. more than 1: Load arm of pliers
  2. equal to 1: See – saw
  3. less than 1: The load arm of a pair of scissors.

Question 19.
Name the class to which the following levers belong:
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 9
Answer:
(a) A pair of scissors — Class I lever
(b) a lemon squeezer — Class II lever
(c) a nut cracker — Class II lever
(d) a pair of sugar tongs — Class III lever
(e) a beam balance — Class I lever
(f) an oar rowing a boat — Class I lever
(g) a wheel barrow — Class II lever
(h) a see saw — Class I lever
(i) a pair of pilers — Class I lever
(j) a crow bar — Class I lever

Question 20.
The diagram given below shows the three kinds of levers. Name the class of each lever and give one example of each class.
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 10
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 11
Examples : The examples of class I levers are : a see saw, a pair of scissors, a pair of pilers, crow bar, common balance, spoon opening the lid of a tin can, handle of a hand pump.
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 12
Examples : The examples of lever of class II are : nut cracker, wheel barrow, paper cutter, mango, lemon squeezer, bottle opener.
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 13
Examples: The examples of levers of class III are : a pair of tongs, sugar tongs, knife, forceps,-forearm of a person holding a load, spade for lifting soil or coal.

Question 21.
Draw diagrams to illustrate the positions of fulcrum, load and effort, in each of the following:
(a) a see saw
(b) a beam balance
(c) a nut cracker
(d) a pair of forceps
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 14

Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 15

Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 16

Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 17

Question 22.
How can you increase the mechanical advantage of a lever ?
Answer:
The mechanical advantage of a lever can be increased by increasing the effort arm or reducing the load arm.

Question 23.
How does the friction at the fulcrum affect the mechanical advantage of the lever ?
Answer:
Friction at the fulcrum reduces the mechanical advantage.

Question 24.
State three differences between the three classes of levers.
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 18

Question 25.
What is a pulley ?
Answer:
Pulley: It is a flat circular disc with a groove in its edge and a rope passing through the groove. It is capable of rotating around a fixed point passing through its central axis called axle.

Question 26.
What is the mechanical advantage of an ideal pulley ?
Answer:
In an ideal pulley, the effort applied is equal to the load to be lifted.
i.e. Effort = Load
Mechanical advantage = Load / Effort = 1

Question 27.
The mechanical advantage of an actual pulley is less than 1. Give a reason. What is the justification for using the pulley then ?
Answer:
In an actual pulley due to friction, the mechanical advantage is less than 1 (i.e. the effort is more than the load).
The reason for using the pulley when its mechanical advantage is equal to 1 or less than 1 is that the pulley allows us to apply the effort downwards i.e. in a convenient direction. To raise a load directly upwards is difficult. But with the help of a pulley, the effort can be applied in the downward direction to move the load upwards. One can hang on it to make use of his own weight also in order to apply the effort.

Question 28.
Draw a neat labelled diagram showing a pulley being used to lift a load. How are load and effort related in an ideal situation?
Answer:
To raise a load, the load is attached to one end of the string and the effort is applied at the other end by pulling it is downward direction . as shown in fig.
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 19

Question 29.
What is an inclined plane? What is its use ? Give two examples where ¡t is used.
Answer:
An inclined plane is a rigid sloping surface over which heavy loads can be raised or lowered to a certain height or depth.
The mechanical advantage of an inclined plane is the ratio of the length of the plank to the vertical height of the load raised. Its value is greater than one. Therefore, an inclined plane acts as a force multiplier. Thus, it can be used to lift heavy loads.
Example : If a heavy box needs to be loaded on a lorry, it is far easier to push it over an inclined plane than to lift it up. Steeper the inclined plane, greater will be the effort required to push up the load.
Sloping ramps, flyovers, roads on hills and staircases are all examples of inclined planes.

Question 30.
What is a screw ? Give two examples.
Answer:
A screw is a simple machine which appears like an inclined plane wound around a rod with a pointed tip.
Examples : ajar lid, a drill.

Question 31.
What is wheel and axle ? Give two examples.
Answer:
The wheel and axle is a simple machine having a wheel and an axle. The linear motion of axle is obtained by rotating the wheel so as to reduce friction. Example: Steering wheel, screw drivers, water tap etc.

Question 32.
How does a wheel help in moving the axle ?
Answer:
Wheel-and-axle arrangement consists of two cylinders of different diameters joined together such that if one is made to rotate, the other also rotates. The axle is a cylindrical rod fixed to the centre of a circular disc-like object called the wheel.
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 20
This machine acts as a speed multiplier device.
In riding a bicycle, when we apply force on the wheel (by pedal), the fixed axle rotates with it easily. This force that turns the axle produces a much larger movement of the wheel.

Question 33.
What is a wedge ? Give two examples.
Answer:
A wedge is a double inclined plane such that the two sloping surfaces taper to form either a sharp edge or a pointed edge. Examples : A knife, an axe, a chisel.
In some special cases, the number of inclined planes used can be more than two as well. In such cases, the sloping surfaces generally taper to form either a very sharp or a pointed edge to split or pierce materials. Pins, nails and needles are examples of pointed wedges. The front end of a boat is shaped like a wedge so that it can easily cut across the flowing water.
The wedge works on a principle of an inclined plane.

Question 34.
Name the machine to which the following belong :

  1. Beam balance
  2. Lemon crusher
  3. Sugar tongs
  4. Ramp
  5. Door knob
  6. Needle

Answer:

  1. Beam balance — A lever (lever of class I)
  2. Lemon crusher — A lever (lever of class II)
  3. Sugar tongs — A lever (lever of class III)
  4. Ramp — An inclined plane
  5. Door knob — Wheel and axle
  6. Needle — Wedge

Question 35.
What care would you take to increase the life span of a machine which you use ?
Answer:
Taking care of machines: Some of the ways in which machines should be cared for are given below :

  1. Machines should be kept in a clean environment, which is free from dust and moisture.
  2. When not in use, machines should be kept covered to prevent collection of dust on them.
  3. Machines made of iron should be protected from rust by coating them with paint.
  4. The moving parts of a machine should be regularly oiled with a good-quality machine oil to reduce friction and wear and tear. The above care of machines increases their life.

Question 36.
Select the correct statement :
(a) A wheel barrow is a lever of class I.
(b) The efficiency of a machine is always 100%
(c) Friction in moving parts of a machine reduces its efficiency.
(d) No lever has the mechanical advantage greater than 1.
(e) It is easier to lift a load vertically up than to push it along an inclined plane.
(f) A screw is made by two inclined planes placed together.
Answer:
(c) Friction in moving parts of a machine reduces its efficiency.

C. Numericals

Question 1.
In a machine an effort of 10 kgf is applied to lift a load of 100 kgf. What is its mechanical advantage ?
Answer:
Given,
Load = loo kgf
Effort = 10 kgf
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 21

Question 2.
The mechanical advantage of a machine is 5. How much load it can exert for the effort of 2 kgf ?
Answer:
Given,
Mechanical advantage = 5
Effort 2 kgf
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 22

Question 3.
The mechanical advantage of a machine is 2. It is used to raise a load of 15 kgf. What effort is needed ?
Answer:
Given,
Mechanical advantage = 2
Load = 15 Kgf
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 23

Question 4.
A lever of length 100 cm has effort of 15 kgf at a distance of 40 cm from the fulcrum at one end. What load can be applied at its other end ?
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 24

Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 25

Question 5.
In a lever, fulcrum is at one end at a distance of 30 cm from the load and effort is at the other end at a distance of 90 cm from the load. Find :
(a) the length of load arm,
(b) the length of effort arm, and
(c) the mechanical advantage of the lever.
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 4 Simple Machines 26

Selina Concise Physics Class 6 ICSE Solutions – Matter

Selina Concise Physics Class 6 ICSE Solutions – Matter

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 6 Physics. You can download the Selina Concise Physics ICSE Solutions for Class 6 with Free PDF download option. Selina Publishers Concise Physics for Class 6 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 6 Physics ICSE SolutionsChemistryBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 6 Physics Chapter 1 Matter

Synposis

  •  Matter is the substance which occupies space and has mass.
  •  The three states of matter are
  1.  solid,
  2.  liquid
  3.  gas.
  •  Matter is composed of large number of molecules.
  •  A molecule is the smallest particle which can exist freely in nature by itself and it retains the properties of the substance.
  •  All molecules of a substance are identical, but the molecules of different substanes are different.
  •  A molecule is very small in size (10-10 m).
  •  The molecules are separated from each other with spaces called inter-molecular spacing.
  •  The molecules in a substance are held together by the forces acting between the molecules which are called the inter-molecular forces.
  •  The force of attraction between the molecules of the same sub¬stance is called the force of cohesion, while the force of attraction between the molecules of two different substances is called the force of adhesion.
  •  The forces of cohesion and adhesion are effective only when the separation between the molecules is 10-9 m. When the separation becomes more, they vanish.
  •  The molecules in a substance are not at rest, but they are con¬stantly in motion.
  •  In a solid, the molecules are rigid, the inter-molecular spacing is least, the inter-molecular forces are strongest and the molecules remain in their fixed positions. They vibrate to and fro about their mean positions, but they do not leave their positions, so a solid has a definite shape and a definite volume.
  •  In a liquid, the molecules are not rigid, the inter-molecular spacing is more than that in solids, the inter-molecular forces are weak and the molecules are free to move within the boundary of the liquid, so the liquid has a definite volume, but it does not have a definite shape.
  •  In gases, the molecules are not rigid, the inter-molecular spacing is more than that in solids and liquids, the inter-molecular forces are weakest and the molecules are free to move anywhere in space. So the gas has neither a definite volume nor a definite shape.

Activity – 2

Classify 20 objects around you as solids, liquids and gases

Solids : Ice, Aluminium, Silver, Calcium, Gold, Iron, Sodium, chloride, Sugar, Wood.

Liquids : Water, benzene, chloroform, oil, honey, glycerine, hydrochloric acid, alcohol, dettol.

Gases : Steam, Air, Oxygen, Hydrogen, Chlorine, Nitrogen, Ammonia, Helium, Argon.

Test yourself

A. Objective Questions

1. Write true or false for each statement

(a) The molecules of each substance are identical.
Answer. False

(b) The inter-molecular forces are effective at all distances between the two molecules.
Answer. False

(c) The molecules in a substance arc in random motion.
Answer. Tme

(d) In a gas, the molecules can move anywhere in space. .
Answer. Tme

(e) The liquids are less viscous than the gases.
Answer. False

2. Fill in the blanks

(a) All the molecules of a substance are identical.
(b) The inter-molecular spacing is least in solids more in liquids and still more in gases.
(c) The molecular motion in liquid and gas is in zig-zag path.
(d) In a solid, the molecules vibrate to and fro but they remain at their fixed positions.
(e) The inter-molecular forces are the weakest in gases.
(f) A solid exerts pressure downwards on its base.
(g) The gases are least dense.
(h) A solid is most rigid.

3. Select the correct alternative

(a) The diameter of a molecule is approximately

  1.  1 cm
  2.  10 cm
  3.  10-10 m
  4.  1 m

(b) The inter-molecular forces are strongest in

  1.  solids
  2.  liquids
  3.  gases
  4.  both (i) and (ii)

(c) The molecules

  1.  in solid, liquid and gas, move freely anywhere.
  2.  in a solid, move freely within its boundary.
  3.  in a liquid, move within its boundary.
  4.  in a gas, move only within its boundary.

(d) The solids are

  1.  more dense
  2.  less dense
  3.  least dense
  4.  highly compressible

(e) The inter-molecular forces in liquids are

  1.  as strong as in solids
  2.  stronger than in solids
  3.  weaker than in solids
  4.  weaker than in gases

4. Match the following columns
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 1

Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 2

B. Short/Long answer questions

Question 1.
Define matter. What is its composition ?
Answer:
Matter is defined as anything which occupies space and has mass. It can be perceived by our sense of smell, touch, sight, hearing and taste.
Matter is composed of tiny particles known as atoms.

Question 2.
Name the three states of matter.
Answer:
The three states of matter are solids, liquids and gases.
Solids —A solid has a definite shape and definite volume.
Example – wood, stone, iron, ice etc.
Liquid —A liquid has a definite volume but not definite shape.
Example — water, juice, milk, oil, etc.
Gases —A gas neither has definite shape nor a definite volume.
Example – air, hydrogen, oxygen, water vapour etc.

Question 3.
What is a molecule ?
Answer:
The smallest unit of matter which can exist independently is called molecule.
Example: Oxygen molecule (O2) made up of two (O) atoms.

Question 4.
What is the approximate size of a molecule ?
Answer:
Matter is made up of molecules which are very small in size (~10-9 m).

Question 5.
One litre of water has 6.02 × 1026 molecules. Estimate the size of a molecule.
Answer:
The size of a particle (or molecule of matter is very small. 1 litre of water has 6.02 × 1026 molecules, so the volume of a particle of
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 3
Thus the diameter of a water molecule is nearly 1.27 × 10-9 metre.

Question 6.
What do you mean by inter-molecular spacing ?
Answer:
Intermolecular space — The space between any two consecutive molecules of a substance is called intermolecular space

Question 7.
Describe a simple experiment to illustrate the existence of inter-molecular spacing.
Answer:
Take 100 ml of water in a measuring cylinder. Add 20 gram of salt in water gently and stir it well so as to dissolve the salt well in water. It is noticed that the level of water does not change. It shows that the particles of salt occupy spaces between the particles of water.
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 4

Question 8.
What do you mean by inter-molecular forces ?
Answer:
Intermolecular force of attraction — The force of attraction between the molecules (like molecules or unlike molecules) is called intermolecular force of attraction.

Question 9.
What are the forces of cohesion and adhesion ?
Answer:
The force of attraction between the molecules of similar kind is called force of cohesion.
Example: The forces between water molecules.
This force of cohesion keep the molecules of the substance bind together.
The force of attraction between different types of molecules is called force of adhesion.
Example: When a glass filled with water is emptied some water I particles remain stuck to the glass due to the adhesion between water molecules and glass.

Question 10.
State three characteristics of molecules of matter.
Answer:
The particles of matter called molecules, have the following characteristics:

  1.  They are very small in size.
  2.  They have spaces between them.
  3.  They are in constant random motion.
  4.  They always attract each other.

Question 11.
State the approximate spacing between two molecules of a matter.
Answer:
The spacing between particles of a matter is called inter-molecular space.

Question 12.
How do the solids, liquids and gases differ in their following properties
(a) Size
(b) Shape
(c) Density
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 5

Question 13.
The molecules in a substance are in motion. What type of path do they follow ?
Answer:
The particles in a substance are not at rest (in motion),and they move randomly in all possible directions in a zig-zag Path

Question 14.
Describe a simple experiment to illustrate that molecules are not at rest, but they constantly move.
Answer:
Take a beaker. Fill it partly with water. Add some lycopodium powder in the beaker containing water. Stir the contents of the beaker with a glass rod. Take out few drops of this suspension on a glass plate. Place it on the table and illuminate it with a table lamp. Observe the glass plate through a microscope. It is found that the fine particles of lycopodium powder move rapidly in a random manner and their path is zig zag as shown in figure below.
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 6

Question 15.
Write down five general properties of solids, liquids and gases.
Answer:
Solids:

  1.  The molecules here are very tightly packed having negligible or very less intermolecular space.
  2.  They have the strongest intermolecular force of attraction.
  3.  The molecules have very small vibration about their mean position i.e. small amplitude.
  4.  They have a definite shape and volume.
  5.  They are generally hard and rigid.
  6.  They are good conductors of heat.

Liquids:

  1.  Molecules are less tightly packed.
  2.  The intermolecular force of attraction is less than that of solids.
  3.  The molecules here can move from one place to another
  4.  Do not have any particular shape of their own and thus acquire the shape of the vessel.
  5.  A particular quantity of a liquid has a definite volume at a given temperature.

Gases :

  1.  The force of attraction between the molecules is the least.
  2.  The intermolecular space is the largest.
  3.  Neither have a definite shape nor a definite volume.
  4.  The molecules move independently.
  5.  Worst conductors of heat.

Question 16.
Give the molecular model for a solid and use it to explain why a solid has a definite volume and a definite shape.
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 7
Here the molecules are very tighty packed that there is no or very less intermolecular space and there is high intermolecular force of attraction (force of cohesion).
The molecules do not move about their mean position and thus solids have a definite shape and volume.

Question 17.
Describe the molecular modcl for a liquid. I-low does it explain that a liquid has no definite shape, but has a definite Volume ?
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 8
Here the molecules are less tightly packed as compared to solids and also there is lesser force of intermolecular attraction. The intermolecular distance is greater than that in the solids. Thus, they do not have a definite shape but acquire the shape of the vessel in which they are contained but have a definite volume at a given temperature.

Question 18.
A gas has neither a definite volume nor a definite shape. Describe the molecular model to explain it.
Answer:
Here the molecules are far apart from each other i.e. have the greatest intermolecular distance which result into the weakest intermolecular forces of attraction. The molecules as are not
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 9
bound by any strong force move about freely and thus gases do not have a definite shape and also do not have any definite volume.

Question 19.
Distinguish between the three states of matter—solid, liquid and gas on the basis of their molecular models.
Answer:
Solids:
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 10
Here the molecules are very tighty packed that there is no or very less inteimolecular space and there is high intermolecular force of attraction (force of cohesion).
The molecules do not move about their mean position and thus solids have a definite shape and volume.
Liquids:
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 11
Here the molecules are less tightly packed as compared to solids and also there is lesser force of intermolecular attraction. The intermolecular distance is greater than that in the solids. Thus, they donot have a definite shape but acquire the shape of the vessel in which they are contained but have a definite volume at a given temperature.
Gases :
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 12
Here the molecules are far apart from each other i.e. have the greatest intermolecular distance which result into the weakest intermolecular forces of attraction. The molecules as are not bound by any strong force move about freely and thus gases do not have a definite shape and also do not have any definite volume.

Question 20.
Distinguish between solids, liquids and gases on the basis of their following properties :
(a) compressibility
(b) fluidity
(c) rigidity
(d) expansion on heating
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 13

Question 21.
What do you mean by the change of state of matter ? Explain:
(a) the change of a solid into a liquid at a constant temperature, and
(b) the change of a liquid into a gas at a constant temperature.
Answer:
The change in state of matter of a substance from solid to liquid or from liquid to gas is brought by imparting heat energy to it at a constant temperature.
(a) The process of change of a substance from solid state into its liquid state on absorption of heat at a particular temperature, called the melting point, is called melting or fusion i. e.
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 14
(b) The process of change of a substance from a liquid state to its gaseous state at a particular temperature, called the boiling point,
is called boiling or vaporisation, i.e.
Selina Concise Physics Class 6 ICSE Solutions Chapter 1 Matter 15

Selina Concise Physics Class 6 ICSE Solutions – Physical Quantities and Measurement

Selina Concise Physics Class 6 ICSE Solutions – Physical Quantities and Measurement

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Selina Concise ICSE Solutions for Class 6 Physics Chapter 2 Physical Quantities and Measurement

  • Synposis
  •  The observation of a phenomenon is made possible by using the five senses: sight, smell, touch, hearing and taste.
  •  Our senses are not always reliable. They are subjective.
  •  Sometimes it is necessary to make an exact measurement.
  •  Physics is a science of measurement.
  •  We use instruments to get an exact measurement.
  •  Four basic measurements in our daily life are: measurement of length, measurement of mass, measurement of time, and measurement of temperature.
  •  Measurement is basically a process of comparison of the given quantity with a standard unit.
  •  For measuring a quantity we need a unit, and then we find the number of times that unit is contained in that quantity.
  •  The unit selected for measurement should be of a convenient size and it must not change ‘with place or time.
  •  The distance between two fixed points is called length.
  •  The S.I. unit of length is metre (m). Its multiple is kilometre (km), where 1 km = 1000 m. Its sub multiples are centimetre (cm) and millimetre (mm), where 1 cm = 10-2 m and 1 mm = 10-3 m.
  •  The FPS unit of length is foot (ft) and its sub multiple is inch where 1 ft = 12 inch and 1 ft = 30.48 cm.
  •  The most common instruments used to measure length are the metre ruler and the measuring tape which are marked in cm and mm.
  •  To measure a length accurately with a metre ruler, the scale should be placed with its markings close to the object and parallel to its r length. The eye is kept in front of and in line with the reading to be taken.
  •  The quantity of matter contained in a body is called its mass.
  •  The S.I. unit of mass is kilogram (kg). Its multiples are quintal and metric tonne. 1 quintal = 100 kg and 1 metric tonne =10 quintal = 1000 kg. Its sub multiples are gram (g) and milligram (mg) where 1 g = 10 kg and lmg = 10-6 kg.
  •  The FPS unit of mass is pound (lb) where 1 lb = 453.59 g.
  •  Mass of a body is measured by using a beam balance or an electronic balance.
  •  The interval between two instances or events is called time.
  •  The S.l. unit of time is second (s), 1 s 1 / 86400 of a mean solar day. The C.G.S. and F.P.S. unit of time is also second (s).
  • The multiple unit of time are minute (mm), hour (h), day and year where 1 min = 60 s, 1 h = 3600 s, 1 day = 86400 s and 1 year = 3.15 × 107 s.
  •  The time at any instant is recorded by a pendulum clock or watch and the time interval of an event is measured by using a stop watch or a stop clock.
  •  The temperature is the measure of degree of hotness or coldness of a body.
  •  The S.I. unit of temperature is kelvin(K), but the common unit of temperature is degree Celsius (°C) and degree fahrenheit (°F).
  •  Doctors use a clinical thermometer to measure the patient’s body temperature.
  •  The normal temperature of a human body is 37°C or 98.6°E
  •  The total surface occupied by an object is called its area. Area is expressed as the product of measured length of two sides.
  •  The S.I. unit of area is square metre (m2).
  •  One square metre is the area of a square of each side one metre.
  •  The bigger (or multiple) units of area are dam2, hectare and square kilometre (km2), where 1 dam2 =100 m2,1 hectare= 104 m2 and 1 km2 = 106  m2
  •  The smaller (or sub multiple) units of area are cm2 and mm2 where 1cm2 = 10-4 m2 and 1 mm2 = 10-6  m2

Test yourself

A. Objective Questions

1. Write true or false for each statement

(a) S.I. unit of temperature is Fahrenheit.
Answer. False

(b) Every measurement involves two things – a number and a unit
Answer. True

(c) Mass is the measure of quantity of matter.
Answer. True

(d) The S.I. unit of time is hour.
Answer. False

(e) The area can be expressed as the product of length of two sides.
Answer. Tme

2. Fill in the blanks

(a) The S.I. unit of length is metre of time is second of mass is kilogram.
(b) °C is the unit of temperature.
(c) 1 metric tonne = 1000 kg
(d) The zero mark in Celsius thermometer is the melting point of ice
(e) The thermometer used to measure the human body temperature is called the clinical thermometer.
(f) The normal temperature of human body is 37 °C or 98.6 °F.
(g) The mass of an object is measured with the help of a beam balance.

3. Match the following columns
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 1
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 4a

4. Select the correct alternative

(a) The symbol of degree celsius is

  1. °C
  2.  °F
  3.  K
  4.  °K

(b) lO mm is equal to

  1.  1cm
  2.  1m
  3.  10dm
  4.  10cm

(c) The amount of surface occupied by an object is called its:

  1.  volume
  2.  area
  3.  mass
  4.  length

(d) A metre ruler is graduated in:

  1.  m
  2.  cm
  3.  mm
  4.  km

(e) A thermometre is graduated in:

  1.  kelvin
  2.  °C
  3.  g
  4.  cm

B. Short/Long Answer Questions

Question 1.
What is measurement ? How is a measurement expressed ?
Answer:
Measurement is a comparison of an unknown quantity with a known fixed quantity of the same kind.
The value obtained on measuring a quantity is called its magnitude. The magnitude of a quantity is expressed as numbers in its unit.

Question 2.
State two characteristics of a unit.
Answer:
Two characteristics of a unit are

  1.  It should be of convenient size.
  2.  It must be universally accepted, i. e. its value must remain same at all places and at all times.

Question 3.
Name four basic measurements in our daily life.
Answer:
In our daily life we measure the following four basic physical quantities.

  1.  Length
  2.  Mass
  3.  lime
  4.  Temperature

Question 4.
What are the S.I. units of

  1.  mass
  2.  length
  3.  time and
  4.  temperature. Write their names and symbols.

Answer:
S.I. units are as follows
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 2

Question 5.
Define one metre, the S.I. unit of length. State its one multiple and one sub multiple.
Answer:
One metre is defined as the distance travelled by light in air in \(\frac { 1 }{ 299,792,458 }\) of a second
Multiple of metre = Kilometre
Submultiple of metre = Centimetre

Question 6.
Convert the following quantities as indicated
(a) 12 inch = ft
(b) 1 ft = cm
(c) 20 cm = m
(d) 4.2 m = cm
(e) 0.2 km = m
(f) 0.2 cm = mm
(g) 1 yard = m
Answer:
(a) 12 inch 1 ft
(b) 1 ft = 30.48cm
(c) 100 cm = 1m
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 3

Question 7.
(a) Describe in steps how would you measure the length of a pencil using a metre rule. Draw a diagram if necessary.
Answer:
To measure the length of a pencil using a metre rule, place metre rule with its marking close to the object. Let PQ be a pencil.
The end P of the pencil coincides with the zero mark on the ruler. The end Q of the pencil is read by keeping the eye at the position ‘B’ vertically above the end Q. So the length of pencil is 4.3 cm.
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 4
(b) Explain with an example how you will use the metre ruler in part (a) if the ends of ruler are broken.
Ans. The ends of the ruler get damaged with use and its zero mark may not be visible. To measure the length of an object with such a ruler, the object is placed close to a specific markings on the ruler and positions of both ends of the object are read on the ruler.
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 5
The difference of the two readings gives the length of the object. In fig. the reading on ruler at the end X is 1.0 cm and at the end Y is 4.3 cm. So the length of the rod XY is 4.3 — 1.0 = 3.3 cm.

Question 8.
Name the device which you will use to measure the perimeter of your play ground. Describe in steps how you will use it.
Answer:
We will use a measuring tape to measure the perimeter of our playground.
To measure the length of playground the tape is spread along the length of the curved area.

Question 9.
The diagram below shows a stick placed along a metre RULER. The length of the stick is measured keeping the eye at positions A, B and C.
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 6
Answer:
(a) Write the length if stick PQ as observed, for each position of the eye. Are they all same?
Ans. Length of stick PQ from
Position A =3.4 cm
Position B = 3.2 cm
Position C = 3.00 cm
No they are not same.
(b) Which is the correct position of the eye? Write the correct length of the stick.
Ans. ‘B’ is the correct position of the eye. Correct length of the stick PQ = 3.2 cm

Question 10.
Define mass. State its (1) S.I. (2) C.GS and (3) EP.S. units. How are they related ?
Answer:
The mass of a body is the quantity of matter contained in it. The S.I. unit of mass is kilogram. In short form, it is written as kg.
In C.GS. system, the unit of mass is gram, (symbol g).
In F.P.S. system, the unit of mass is pound (symbol lb)

Question 11.
Convert the following quantities as indicated:
(a) 2500 kg = ………. metric tonne.
(b) 150 kg = quintal
(e) 10 lb = ………. kg
(d) 250 g = … .kg
(e) 0.01 kg = ………. g
(f) 5 mg = ………. kg
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 7

Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 8

Question 12.
Name the instrument which is commonly used to measure the mass of a body. State how is it used ?
Answer:
Instrument commonly used to measure the mass of a body, is the beam balance.
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 9
When we hold up the balance, we observe that when there is nothing on either pan, the beam is horizontal. The body whose mass is to be measured is placed on the left pan. The standard weight are put on the right pan. They are so adjusted that the beam is again horizontal on holding the balance up. The total of the standard weights gives the mass of the given body.

Question 13.
Define one kilogram, the S.I. unit of mass. How is it related to (i) quintal (ii) metric tonne and (iii) gram.
Answer:
The mass of 1 litre of water at 4 °C is taken as 1 kilogram
1 quintal = 100 kg
1 metric ton = 10 quintal = 1000 kg

Question 14.
Name and define the S.I. unit of time. How is it related to (i) minute (ii) hour, (iii) day and (iv) year ?
Answer:
The S.I. unit of time is second. In short form we write it as ‘ S ’.
One second is the time interval between the two consecutive ticks that you hear from pendulum wall clock.
1 min = 60 s
1 h = 60 min. = 3600 s.
1 day = 24 h = 86400 s.
1 year = 365 days = 3.15 × 107 s.

Question 15.
Name two devices used to measure the short time interval of an event.
Answer:
Two devices used to measure the time interval of an event are

  1.  StopWatch
  2.  Stop Clock

Question 16.
Express in second

  1.  3 minute 15 second and
  2.  5 hour 2 minute 5 second.

Answer:

  1.  3 minute = 15 second
    1 minute = 60 second
    3 minutes 15 second = 60 × 3 + 15
    = 180 + 15
    = 195 seconds
  2.  1 minute =60 second
    2 minutes =2 × 600 = 120 second …(1)
    1 hour 3600 second
    5 hour 3600 × 5 = 18000 second …(2)
    5 hour 2 minutes and 5 second
    = 18000 + 120 + 5 = 18125 seconds

Question 17.
What does the temperature measure ?
Answer:
Temperature measures the degree of coldness and hotness of a body.

Question 18.
Name the

  1.  S.I. unit and
  2.  one common unit of temperature. Write their symbols also.

Answer:
The S.I. unit of temperature is kelvin (symbol K).
Common unit of temperature is degree centigrade (symbol °C)

Question 19.
Name the instrument used for measuring of the temperature of a person. Draw its labelled neat diagram.
Answer:
The temperature is measured with a thermometer.
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 10

Question 20.
Write the temperature of (i) melting ice (ii) boiling water.
Answer:
The temperature of

  1.  melting ice = 0 °C
  2.  boiling water = 100 °C

Question 21.
What is a clinical thermometer ? State its special feature. Draw a labelled neat diagram of a clinical thermometer showing the range of temperature marked on it.
Answer:
Doctors use a special thermometer called the clinical thermometer for measuring the temperature of the patient’s body. This thermometer has the markings from 35°C to 42°C. It has a slight bend or kink in the stem just above the bulb. This kink is called the constriction. This constriction prevents the mercury from falling back all by itself. The temperature of a healthy person is 37°C. This temperature is marked by a red arrow.
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 11

Question 22.
What is the normal temperature of the human body ? How is it indicated in a clinical thermometer ?
Answer:
Normal temperature of a human body is 37°C or 98.6 °F.
To measure the temperature of a patient’s body, its bulb is kept either below the tongue or under the arm’s pit of the patient for about a minute. Then the thermometer is taken out and its reading is noted. When the temperature of patient’s body is above 37°C, he is said to suffer with fever.

Question 23.
Can a clinical thermometer be used to measure the temperature of the boiling water ? Give reason for your answer.
Answer:
No, a clinical thermometer cannot be used to measure the temperature of boiling water. ,
The reasons are

  1.  It has a very small range.
  2.  It can break on cooling and on excess heating.

Question 24.
Explain the term ‘area of a surface’.
Answer:
The total surface occupied by an object is called its area or surface area.

Question 25.
Name the S.I. unit of area and define it.
Answer:
The S.I. unit of area is square metre or meter2 which in short form is written as m2.

Question 26.
How are the units

  1.  square yard
  2.  hectare
  3. km2
  4. cm2
  5. mm2 related to the S.I. unit of area ?

Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 2 Physical Quantities and Measurement 12

Question 27.
Explain how you will measure the area of (i) a square (b) a leaf?
Answer:
The area of a square can be calculated by using the following formula –
1. Area of square of side l
= side x side
= l × l = L2 .
The area of a leaf is obtained by using a graph paper. A graph paper has small squares of each side 1 mm. The area of each big square is 1 cm2.
Procedure: Place the leaf on graph paper. Draw its outline on the paper and remove it. Now count the number of complete squares. To this add the number of incomplete squares which are half or more than half. Ignore the squares which are less than half. Thus,
Approximate area = (No. of complete squares + no. of half or more than half of incomplete squares) × area of one square.