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Selina Concise Physics Class 6 ICSE Solutions – Magnetism

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Selina Concise ICSE Solutions for Class 6 Physics Chapter 6 Magnetism

• Synposis
• The first natural magnet was discovered in Magnesia, a town in Greece. It was called the lodestone.
• Artificial magnets are made of iron or steel. They are made of different shapes namely the bar magnet, cylinderical magnet, U-shaped magnet, horse-shoe magnet, magnetic needle and compass.
• The materials which are attracted by a magnet are called magnetic materials. Examples: iron, steel, cobalt.
• The materials which are not attracted by a magnet are called non-magnetic materials. Examples: paper, wood, brass, plastic, copper aluminium, etc.
• A magnet has two poles, a north and a south pole.
• A magnet has the following properties:

1. A magnet attracts the small pieces of iron.
2. A magnet always rests in the north-south direction, if it is free to swing.
3. Like poles repel each other and unlike poles attract each other.
4. Poles always exist in pairs, cannot be isolated.

• Magnets are used to separate iron and steel from their mixture with non-magnetic substances. –
• Magnets are used in many electrical appliances such as electric . bell, loud-speaker, etc.
• A magnetic compass is used by sailors and navigators to find the north-south direction.
• Magnetic induction is the process in which a piece of iron temporarily behaves like a magnet in the presence of another magnet.
• When a magnet is placed near an iron piece, the iron piece behaves like a magnet. The end of the iron piece near the north pole of the magnet becomes a south pole while the farther end becomes a north pole.
• It is because of magnetic induction that a magnet attracts a piece of iron.
• An iron piece can be made into a magnet by any of the following methods:

1. Magnetic induction
2. Single touch method
3. Double touch method
4. Electrical method

• In the single touch method, we need a single magnet, but in the double touch method we need two magnets, hi these methods, the end touched last by the magnet has the polarity opposite to that of the striking pole.
• Powerful magnets are made by the electrical method.
• Electromagnets or temporary magnets are made of soft iron.
• Permanent magnets are made of steel.
• Electromagnets are used in devices like electric bell, magnetic toys, telephone etc.
• Permanent magnets are used in devices like galvanometer, ammeter, voltmeter etc.
• A magnet can be destroyed by rough handling, by dropping it several tunes, by hammering it repeatedly and by heating it.
• The magnetic field around a magnet is the space in which a magnetic substance such as small iron piece experiences a force of attraction.
• The earth itself behaves like a magnet. It has its own magnetic field.
• The south polarity of the earth is near the geographic north pole and the north polarity of the earth is near the geographic south pole.
• Magnetic keepers are used to store the magnets.
• Magnetic keepers are small pieces of soft iron.

ACTIVITY 1

Magnetic objects
Iron, Steel, Cobalt, Nickel
Non-magnetic objects
Wood, Stone Plastic, Rubber Copper, Sand, Gold, Silver, Brass Paper, Aluminium

Test yourself

A. Objective Questions

1. Write true or false for each statement.

(a) Artificial magnets are weaker than the natural magnets.
Answer. False
Artificial magnets are stronger than the natural magnets.

(b) Poles of a magnet cannot be separated.
Answer. True

(c) A magnet can attract only a magnetic substance.
Answer. True

(d) A magnet has no effect when it is heated to a high temperature.
Answer. False.
A magnet get demagnetised when it is heated to a very high temperature.

(e) Permanent magnets get easily demagnetised.
Answer. False.
Permanent magnets cannot be demagnetised.

(f) Magnetic poles occur in pairs.
Answer. True

(g) Single touch method is better than the electrical method for making a magnet.
Answer. False.
Electrical method is better than single touch method.

(h) Magnetic keeper is a wooden piece.
Answer. False.
Magnetic keepers are the pieces of soft iron.

(i) Copper cannot be magnetised.
Answer. True

2. Fill in the blanks

(a) Temporary magnets are usually made up of soft iron.
(b) Rough handling destroys the magnetic properties of a magnet.
(c) Like poles repel each other.
(d) A freely suspended magnet points in the north-south direction.
(e) In a magnet, ends have the maximum attractive property.
(f) A magnet has two poles.

3. Match the following

4. Select the correct answer

(a) If we suspend a magnet freely, it will settle in .

1. east-west direction
2. north-south direction
3. north-east direction
4. east-south direction

(b) Making a magnetic substance a magnet by bringing it closer to another magnet without touching it, is

1. magnetic induction method
2. single touch method
3. double touch method
4. electrical method

(c) An example of natural magnet is

1. iron
2. steel
3. lodestone
4. none of above

(d) The artificial magnet used to detect direction in the laboratory is

1. U-shaped magnet
2. horse shoe magnet
3. electromagnet
4. magnetic compass

B. Short/Long Answer Questions

Question 1.
What is a magnet ?
Answer:
The substances which have the property of attracting iron, are called magnets.

Question 2.
What are magnetic and non-magnetic substances ? Give two examples of each.
Answer:
Magnetic substances: The substances that get attracted by a magnet are called magnetic substances. Iron, steel, cobalt and nickel are magnetic substance
Non-magnetic substances : The substances that do not get attracted by a magnet are called non-magnetic substances, e.g., wood, plastic, copper, paper, aluminium, rubber, stone.

Question 3.
What are natural and artificial -magnets ?
Answer:
Natural magnets: Natural magnets are those which are found in nature e.g. load stone.
Artificial magnets: Man made magnets are called artificial magnets, e.g. electromagnet.

Question 4.
How is an artificial magnet prepared from a natural magnet ?
Answer:
Pieces of iron or other materials are made magnets by rubbing them with natural magnets (or by passing direct current through a wire wound around them). This is how artificial magnets are made.

Question 5.
State two ways of magnetising an iron piece.
Answer:
The two ways of magnetising an iron piece are:

1. Magnetic induction method.
   Take a long iron nail and test it for magnetic properties by bringing near the magnetic substances. You will see nail does not attract the magnetic substances. Now bring near a pole of a bar magnet to the head of the nail. Now bring the iron paper clips near the pointed end of the nail, you will observe that the iron paper clips now get attracted towards the nail. This is because iron nail has become magnet. Now take the bar magnet away form the iron nail, paper clips fall off. This magnetism is temporary.
   
2. Single touch method: Take a demagnetised piece of iron. Place it on a table surface. Take a magnet and select its one pole. Now mb it with the selected pole on the iron in one direction for several times. After sometime, the iron piece turns into a magnet.
   

Question 6.
How can magnetic properties of a magnet be destroyed ?
Answer:

1. By hammering the magnet repeatedly.
2. By rough handling
3. By heating.

Question 7.
Why docs a freely suspended magnet always rest in north- south direction ?
Answer:
A freely suspended magnet always rest in north-south direction because the north-pole of the magnet lies in the geographic north direction and the south pole of the magnet lies in the geographic south direction. So it aligns itself in N-S direction. As unlike poles attract and like poles repel.

Question 8.
Draw diagrams of the artificial magnets of four different shapes.
Answer:

Question 9.
Why are the artificial magnets preferred over the natural magnets ?
Answer:
Artificial magnets are preferred over natural magnets because natural magnets are weak and often irregular in shape, they can readily be magnetised and demagnetised by turning the current on or off in the coil.

Question 10.
Describe an experiment to show that the maximum attractive property is at the poles of a magnet.
Answer:
Take a bar magnet and place a steel pin at some distance. We observe that nothing happens. Now, bring the steel pin near the pole of the bar magnet. We notice that pin sticks to the magnet. This experiment shows that maximum magnetic force acts at the poles of the magnet.

Question 11.
State four important properties of a bar magnet.
Answer:

1. Attractive property: A magnet can attract small pieces of iron filing or other ferromagnetic materials.
2. Directive property: If a magnet is suspended horizontally by a thin thread (say silk thread), it rests always pointing north- south direction of earth.
3. Like poles always repel each other and unlike poles attract each other.
4. Poles always exist in pairs : Single pole can never exist.

Question 12.
Explain the attractive property of a magnet with the help of an experiment.
Answer:
Take iron filling on a piece of paper. Bring a bar magnet near it. Iron filling will cling to it. It shows the attractive property of magnet.

Question 13.
Describe the method by which an iron bar can be made a magnet.
Answer:
Single touch method : Place the iron bar (or the needle) AB on a table. Take a bar magnet NS and place it almost vertical with its north pole (N) on the end A of the bar.
Move the magnet along tire iron bar till the other end B is reached.

Lift the magnet at the end B and again place it on the first end A Again stroke the bar. Repeat the process about 20 times. Then turn the iron bar AB upside down. Again stroke it with the magnet about 20 times. The bar now becomes a magnet.

Question 14.
How are the magnets kept safely ? What is the role of keepers in storing the magnets ?
Answer:
When magnets are not in use they should be kept and stored in magnetic keepers. The magnetic keeper are the pieces of soft iron. A magnetic keeper has a card board with one or two iron soft pieces. Two magnets are placed in such a way that their opposite poles are close to each other and then a soft iron keeper is attached with it.

Question 15.
Define the term magnetic field of a magnet. How will you recognise it experimentally ?
Answer:
The space around a magnet in which if a magnetic substance such as small pieces of iron, are placed, they get attracted to-wards the magnet, is called the magnetic field.
Recognition of the magnetic field around a magnet: If a magnet is placed below a sheet of stiff paper and some iron filings are spread on it, then on tapping the sheet gently, the iron filings are found to arrange themselves in a definite pattern as shown in fig.

Question 16.
How will you make an iron bar electromagnet ? Draw a diagram showing the polarities of the electromagnet.
Answer:
Take the given iron bar AB. Wound several turns of insulated copper wire over the bar. Connect the ends of the wire to a battery through a switch. Press the switch to pass current. After some time, the bar AB becomes a magnet.

The end A of the bar at which the current enters the coil in clock¬wise direction becomes the south pole (S) and the end B of the bar at which the current leaves the coil in anti-clockwise direction becomes the north pole (N).

Question 17.
State two ways of increasing the strength of an electro Magnet
Answer:
Strength of the electromagnet: The strength of the electromagnet can be increased:

1. by increasing the current in the coil, and
2. by increasing the total number of turns of the coil.

Question 18.
Suppose you are given a long bar magnet and you are asked to break it into four small magnets. Draw diagrams showing the polarities of each broken part.
Answer:

Question 19.
State three important uses of a magnet.
Answer:
Use of magnet:

1. Magnets are used in magnetic compass, door bells, refrigerators.
2. Magnets are used in dynamos, motors, loudspeakers, microphones etc.
3. Ceramic magnets are used in computers.
4. Magnets are used in toys to give magic effect.

Question 20.
What is magnetic induction ? Explain with the help of a diagram.
Answer:
Magnetic Induction: The property by which an ordinary piece of iron acquires magnetic properties temporarily due to the pres¬ence of another magnet close to it, is known as magnetic induction
Take a long nail. Put it on the arm of a stand. Spread some iron pins on the base of stand. You will find that the pins do not get attracted towards the nail. Now touch a magnet at the end of nail. As the end is brought close to the head of nail, some pins cling to the nail. It happens because the nail turns into magnet and acquires the properties of magnetism. The moment you remove the magnet from the head of the nail. The pins will fall down. It will no more be a magnet.

Question 21.
In which direction does a suspended bar magnet come to rest? Give reason.
Answer:
A magnet always rests in North and South direction, i.e. N-end always towards North of Earth and S-end towards South of Earth.

Question 22.
State three differences between the temporary and permanent magnets.
Answer:
Temporary magnet

1. It is made up of soft iron.
2. The magnet which loses its magnetism as soon as magnetising force is removed away from it.
3. Because of its weak power, it is not used to make iron piece into magnet.

Permanent magnets

1. It is made up of steel, cobalt and nickel.
2. The magnet, which does not lose its magnetic properties easily is called permanent magnet.
3. It can convert ordinary piece of iron into a temporary magnet.

Question 23.
State three ways of demagnetising a magnet.
Answer:
A magnet can be demagnetized in the following ways 

1. rough handling
2. hammering the magnet several times.
3. passing an alternating current around the magnet.
4. dropping the magnet on the floor several times.
5. heating the magnet to a very high temperature.

Question 24.
Suggest one way to recognise the magnetic field of the earth.
Answer:
If we suspend a magnet such that it is free to swing, we see that it always rests in the north-south direction. The north pole of the magnet lies in the geographic north direction and the south pole of the magnet lies in the geographic south direction. So it aligns itself in N-S direction.

Question 25.
Name the material of core of an electromagnet for

1. temporary magnet
2. permanent magnet.

Answer:

1. They are made of soft iron.
2. They are made of iron, steel, cobalt, nickel or an alloy called ANILCO.

Question 26.
You are given an iron nail, a torch cell and a long piece of insulated copper wire. With the help of a labelled neat diagram, describe in steps how you will make the nail, an electromagnet.
Answer:
Aim : To make an electromagnet.
Materials Required : An iron nail, a battery, a switch, some insulated copper wire and some iron paper pins.
Procedure : Coil the insulated copper wire around the iron nail. Connect the ends of the wire to the battery through the switch. Close the switch so that electric current flows through the copper wire. Now bring the iron paper pins close to the iron nail.
Observation And Conclusion : The paper pins get attracted to the nail, showing that the nail has turned into an electromagnet. Now, if you switch off the current, the iron paper pins will drop off the iron nail.

Question 27.
Describe an experiment to illustrate that like poles repel while the unlike poles attract.
Answer:

1. Take two bar magnets A and B. Suspend one magnet A with a silk thread from a support so that it is free to swing. The magnet will come to rest in the north-south direction. The north pole of the magnet is in the north direction and the south pole of the magnet is in the south direction.
2. Now holding the other magnet B in your hand, bring its north pole near the north pole of the suspended magnet A (such that the two magnets do not touch each other) as shown in figure. You will observe that the suspended magnet A moves away from the magnet B. This shows that the like poles repel each other.
   

Now bring the south pole of the magnet B near the north pole of the suspended magnet A as shown in figure, without touching it. You will observe that the magnet A moves towards the magnet B. This shows that the unlike poles attract each other.

Question 28.
What are magnetic keepers ? Name its material.
Answer:
Magnetic keepers are used to store the magnets. Magnetic keepers are small pieces .of soft iron.

Question 29.
How are the north and south poles of a magnet located ? Explain.
Answer:
Suspend a bar magnet with a silk thread from a wooden stand as shown in figure. The magnet swings for some time and then eventually comes to rest in a particular direction i.e., north-south direction. If we disturb the magnet a little, the magnet again comes to rest in the north-south direction.

The end of the magnet which points towards the north is called the north seeking pole or simply the north pole and the end which points towards the south is called the south seeking pole or simply the south pole. The north and south poles are marked by the letters N and S respectively.

Selina Concise Physics Class 7 ICSE Solutions – Physical Quantities and Measurement

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 7 Physics. You can download the Selina Concise Physics ICSE Solutions for Class 7 with Free PDF download option. Selina Publishers Concise Physics for Class 7 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 7 Physics ICSE SolutionsChemistryBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 7 Physics Chapter 1 Physical Quantities and Measurement

• Points to Remember
• The mass of a body is the quantity of matter contained in a body regardless of its volume or any force acting on it.
•  The weight of a body is the force with which every body is attracted towards its centre.
•  The unit of mass in S.I. system is kilogram (kg). Higher units of mass are quintal and metric tonne.
•  The weight of body changes with acceleration due to gravity.
•  Weight is zero at the centre of the earth.
•  Mass per unit volume of a substance is called density of the body.
•  The unit of density in S.I. system is kg m^-3 and gcm^-3 in C.G.S. system.
•  The density in S.I. system is 1000 × numerical value in C.G.S. system.
•  The density of liquids and gases decreases or increases with the rise or fall in temperature.
• The cycle of upward and downward movements of the fluid form currents in the medium which are known as convectional currents.

Test Yourself

A. Objective Questions 

1. Write true or false for each statement

(a) The S.I. unit of volume is litre.
Answer. False.
The S.I. unit of volume is cubic metre.

(b) A measuring beaker of capacity 200 ml can measure only the volume. 200 ml of a liquid.
Answer. True.

(c) cm2 is a smaller unit of area than m².
Answer. True.

(d) Equal volumes of two different substances have equal masses.
Answer. False.
Equalvolumes of two different substances have different masses.

(e) The S.I. unit of density is g cm^-3.
Answer. False.
The S.I. unit of density is Kg m^-3.

(f) 1 g cm^-3 = 1000 kg m^-3.
Answer. True.

(g) The density of water is maximum at 4°C.
Answer. True.

(h) The speed 5 ms^-1 is less than 25 km h^-1.
Answer. True.

(i) The S.I. unit of speed is ms^-1.
Answer. True

2. Fill in the blanks

(a) l m³ = 10⁶ cm³
(b) The volume of an irregular solid is determined by the method of displacement of liquid.
(c) Volume of a cube = (one side)
(d) The area of an irregular lamina is measured by using a grapl paper.
(e) Mass = density × volume.
(f) The S.I. unit of density is kg m^-3.
(g) 1 g cm^-3 = 1000 kg m^-3.
(h) 36 km h^-1 = 10 ms^-1.
(i) Distance travelled d = speed v × time t.

3. Match the following

4. Select the correct alternative 

(a) One litre is equal to :

1.  1 cm^-3
2. 1 m³
3.  10^-3  cm³
4. 10^-3 m³

(b) A metallic piece displaces water of volume 15 ml. The volume of piece is :

1.  15 cm³
2.  15 m³
3.  15 × 10³ cm³
4.  15 × 10³ cm³

(c) A piece of paper of dimensions 1.5 m x 20 cm has area :

1.  30 m2
2.  300 cm2
3.  0.3 m2
4.  3000 m3

(d) The correct relation is :

1.  d = M × V
2.  M = d × Y  
3.  V = d × M
4.  d = M + V

(e) The density of alcohol is 0.8 g cm-3. In S.I. unit, it will be :

1.  0.8 kg m^-3
2.  0.0008 kg m^-3
3.  800 kg m^-3
4.  8 x 10³ kg m^-3

(f) The density of aluminium is 2.7 g cm-3 and of brass is 8.4 g cm^-3. For the same mass, the volume of:

1.  both will be same
2.  aluminium will be less than that of brass
3.  aluminium will be more than that of brass
4.  nothing can be said.

(g) A block of wood of density 0.8 g cm^-3 has a volume of 60 cm³. The mass of block will be :

1.  60.8 g
2.  75 g
3.  48 g
4.  0.013 g

(h) The correct relation for speed is

1.  Speed = distance x time
2.  speed = distance / time
3.  speed = time / distance
4.  speed = 1 / distance x time

(i) A boy travels a distance 150 m in 1 minute. His speed is

1.  150 m s^-1
2.  2.5 m s^-1
3.  25 m s^-1
4.  9 m s^-1

B. Short/Long Answer Questions

Question 1.
Define the term volume of an object.
Answer:
The space occupied by an object is called its volume.

Question 2.
State and define the S.I. unit of volume.
Answer:
S.I. unit of volume – The S.I. unit of volume is cubic metre. In short form, it is written as m³.
One cubic metre is the volume of a cube of each side 1 metre as shown in figure below i.e., 1 m³ = 1 m × 1 m × 1 m.

Question 3.
State two smaller units of volume. How are they related to the S.I. unit?
Answer:
A smaller unit of volume is cubic centimetre (symbol cm³) and cubic decimetre (symbol 1 dm³). One cubic centimetre is the volume of a cube of each side 1 centimetre, i.e.,
1 cm³ = 1 cm × 1 cm × 1 cm.
Relationship between m³ and cm³
l m³ = lm × lm × lm
= 100 cm × 100 cm × 100 cm
= 10,00,000 cm³ = 10⁶ cm³.
Relationship between m³ and dm³
l m³ = lm × 1 m × 1 m .
= 10 dm × 10 dm × 10 dm
= 1000 dm
= 10³ dm
Note 1 m = 10 dm

Question 4.
How will you determine the volume of a cuboid ? Write the formula you will use.
Answer:
Volume of a cuboid = length × breadth × height.

Question 5.
Name two devices which are used to measure the volume of an object. Draw their neat diagrams.
Answer:
Two devices that are used to measure the volume of an object are :
(i) Measuring cylinder and
(ii) Measuring beaker.

Question 6.
How can you determine the volume of an irregular solid (say a piece of brass) ? Describe in steps with neat diagrams.
Answer:
To measure the volume of a piece of stone.
Take a piece of brass, a measuring cylinder, fine thread of sufficient length and some water.
Place a measuring cylinder on a flat horizontal surface and fill it partially with water. Note the reading of the water level very carefully. Now tie the piece of brass with a thread and dip it completely into water. We see that the level of water rises. Note the reading of the new water level.

The difference in the two levels of water gives the volume of the piece of brass
Initial level of water = 60 ml
Level of water when brass is immersed = 80 ml
∴ Volume of water displaced = 80 ml – 60 ml = 20 ml
∴ Volume of the piece of brass = 20 cm³
Note : 1 ml = 1 cm³

Question 7.
You are required to take out 200 ml of milk from a bucket full of milk. How will you do it ?
Answer:
By using the measuring beaker A measuring beaker is used to measure a fixed volume of liquid from a large volume. Suppose it is required to measure 200 ml of milk from the milk contained in a bucket. For this, take the measuring beaker of capacity 200 ml. Wash it and dry it. Then, immerse the measuring beaker well inside the milk contained in the bucket so that the beaker gets completely filled with the milk.
Take out the measuring beaker from the bucket gently so that no milk splashes out and then pour the milk from the measuring beaker into the another empty vessel.

Question 8.
Describe the method in steps to find the area of an irregular lamina using a graph paper.
Answer:
Method to find the area of an irregular lamina using a graph paper : First, place the lamina over a graph paper and draw its boundary line on the graph paper with a pencil. Then remove the lamina and count and note the number of complete squares as well as the number of squares more than half within the boundary line (only the squares less than half, are left while counting). The area of lamina is equal to the sum of the area of complete squares and the area of squares more than half. Let n be the total number of complete and more than half or half squares within the boundary of lamina. Since area of one big square is 1 cm × 1cm = 1 cm², so the area of lamina will be n x

Question 9.
Define the term density of a substance.
Answer:
The density of a substance is defined as the mass of a unit volumx of that substance.

Question 10.
State the S.I. and C.G.S. units of density. How are they inte related ?
Answer:
The S.I. unit of mass is kilogram (symbol kg) and of volume is
cubic metre (symbol m³). Therefore S.I. unit of density is kg/m³
or kg m^-3.
The C.G.S. unit of mass is gram (symbol g) and of volume is cubic centimetre (symbol cm3). Therefore the C.G.S. unit of
density is g/cm³ or g cm^-3.

Question 11.
‘The density of brass is 8.4 g cm’3’. What do you mean by the statement ?
Answer:
Density of brass is 8.4 g cm^-3. This means that unit volume of brass contain 8.4 g mass.

Question 12.
Arrange the following substances in order of their increasing density:
(a) iron
(b) cork
(c) brass
(d) water
(e) mercury
Answer:
b<a<c<d<e

Question 13.
How does the density of water changes when :
(a) it is heated from 0°C to 4°C,
(b) it is heated from 4°C to 10°C ?
Answer:
(a) Water contracts on heating from 0°C to 4°C and expands on heating above 4°C.
(b) The density of water is maximum at 4°C. It decreases when it is cooled from 4°C to 0°C or it is heated above 4°C.

Question 14.
Write the density of water at 4°C.
Answer:
The density of water at 4°C is 1.0 g cm^-3, or 1,000 kg m^-3

Question 15.
Explain the meaning of the term speed.
Answer:
The distance covered or travelled by a body in one second is called the speed of the body, i.e.

Question 16.
Write the S.I. unit of speed.
Answer:
The S.I. unit of speed is metre/second or metre per second. Its symbol is m s^-1.

Question 17.
A car travels with a speed 12 m s”1, while a scooter travels with a speed 36 km h-1. Which of the two travels faster ?
Answer:
Speed of car = 12 m s^-1
Speed of scooter = 36 km h^-1
here, 1 km = 1000 m
1 hr = 3600 sec

∴ Speed of car is more. Car travels faster than scooter.

C. Numericals

Question 1.
The length, breadth and height of a water tank are 5 m, 2.5 m and 1.25 m respectively. Calculate the capacity of the water tank in (a) m³ (b) litre.
Answer:
Given,
Length (1) = 5m
Breadth (b) = 2.5 m
and Height (h) = 1.25 m

Question 2.
A solid silver piece is immersed in water contained in a measuring cylinder. The level of water rises from 50 ml to 62 ml. Find the volume of silver piece.
Answer:
Given, initial level of water .v₁ = 50 ml
Final level of water v₂ = 62 ml
Volume of silver piece V = v₂ – v₁
= 62 ml – 50 ml
= 12 ml or 12 cm³

Question 3.
Find the volume of a liquid present in a dish of dimensions 10 cm x 10 cm x 5 cm.
Answer:
Volume of water = Length × breadth × height
= 10 cm × 10 cm × 5 cm
= 500 cm³ or 500 ml.

Question 4.
A rectangular field is of length 60 m and breadth 35 m. Find the area of the field.
Answer:
Length of a rectangular field = 60 m
Breadth of rectangular field = 35 m
∴ Area = 60 m × 35 m
= 2100 m²

Question 5.
Find the approximate area of an irregular lamina of which boundary line is drawn on the graph paper shown in fig. 1.16. below.

Answer:
From figure, the number of complete squares = 11
The number of squares more than half = 9
∴ Total number of squares = 11 + 9 = 20
∴ Area of the 1 square = 1 cm × 1cm = 1 cm²
∴ Area of 20 squares = 20 × 1 cm² = 20 cm²
∴ Approximate area of irregular lamina = 20 cm²

Question 6.
A piece of brass of volume 30 cm³ has a mass of 252 g. Find the density of brass in (i) g cm^-3, (ii) kg m^-3.
Answer:

Question 7.
The mass of an iron ball is 312 g. The density of iron is 7.8 g cm^-3. Find the volume of the ball.
Answer:

Question 8.
A cork has a volume 25 cm³. The density of cork is 0.25 g cm^-3. Find the mass of cork.
Answer:

Question 9.
The mass of 5 litre of water is 5 kg. Find the density of water in g cm^-3.
Answer:

Question 10.
A cubical tank of side 1 m is filled with 800 kg of a liquid. Find: (i) the volume of tank, (ii) the density of liquid in kg m^-3.
Answer:

Question 11.
A block of iron has dimensions 2 m × 0.5 m × 0.25 m. The density of iron is 7.8 g cm^-3. Find the mass of block.
Answer:
Given, l = 2m
b = 0.5 m

Question 12.
The mass of a lead piece is 115 g. When it is immersed into a measuring cylinder, the water level rises from 20 ml mark to 30 ml mark.
Find:
(i) the volume of the lead piece,
(ii) the density of the lead in kg m^-3.
Answer:

Question 13.
The density of copper is 8.9 g cm^-3. What will be its density in kg m^-3 ?
Answer:

Question 14.
A car travels a distance of 15 km in 20 minute. Find the speed of the car in (i) km h^-1, (ii) m s^-1.
Answer:
Distance travelled by car =15 km
Time taken = 20 minutes
(i) Speed of car in km h^-1
Convert 20 minutes to hour

Question 15.
How long a train will take to travel a distance of 200 km with a speed of 60 km h^-1 ?
Answer:
Distance covered by train = 200 km
Speed of train = 60 km h^-1

Question 16.
A boy travels with a speed of 10 m s^-1 for 30 minute. How much distance does he travel ?
Answer:
Speed of boy = 10 m s^-1
Time taken = 30 minutes
speed = distance travelled / time taken
Distance travelled = Speed × Time taken
Convert 30 minutes to seconds
1 minute = 60 sec
30 minute 60 × 30 = 1800 seconds
Putting the value of speed and time we get
Distance travelled = 10 ms^-1 × (1800 sec) = 18000 m
= 18000 metre or 18 km Ans.

Question 17.
Express 36 km h^-1 in m s^-1
Answer:

Question 18.
Express 15 m s^-1 in km h^-1.
Answer: