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Selina Concise Biology Class 8 ICSE Solutions – Ecosystems

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Selina Concise Biology Class 8 ICSE Solutions – Ecosystems

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APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Biology Chapter 4 Ecosystems. You can download the Selina Concise Biology ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Biology for Class 8 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 8 Biology Chapter 4 Ecosystems

REVIEW QUESTIONS

Multiple Choice Questions:

1. Put a tick mark (✓) against the correct alternative in the following statements:

a. The term “ecosystem” is derived from the Greek word “Oikos” meaning.

  1. Body weight
  2. Food
  3. House
  4. Size

b. Rat in any food chain would occupy the position of

  1. Tertiary consumer
  2. Secondary consumer
  3. Primary consumer
  4. Producer

c. Evergreen broad-leaved trees are characteristic of

  1. Tropical rain forests
  2. Temperate deciduous forests
  3. Coniferous forests
  4. All of the above types of forests.

Short Answer Type:

1. Mention if the following statements are true (T) or false (F).
(a) Snakes are primary consumers (T/F)
(b) Some humans are strictly primary consumers & some others are of other types of consumers also (T/F)
(c) No ecosystem can survive without light (T/F)
(d) Cattle go to ponds for drinking water, so they are a constituent of pond ecosystem (T/F)

Answer:

(a) Snakes are primary consumers (F)
No the snakes are not primary consumers as snakes eat rats and frogs as these are primary consumers which eat plant products. As snakes eat the primary consumers so the snakes are secondary consumers.

(b) Some humans are strictly primary consumers and some others are of other types of consumers also (T)
It is true that humans are vegetarians and eat plants or plant products. So these humans are vegetariBut there are certain humans which eat the flesh or eggs of other animals. These are carnivores and humans living plants are called Herbivores.

(c) No ecosystem can survive without light (T)
The plants and animals and micro-organisms present at a place and interacting with the atmosphere like sun light, air, water, soil and warmth and dwelling at a place like, pond, desert, forest, rock form the ecosystem as pond ecosystem, desert ecosystem forest ecosystem. So ecosystem cannot survive without the presence of light. As the flora (plants) living in that ecosystem can only make food in the presence of light and the animals (Fauna) living in that ecosystem get the food from the plants of that ecosystem. So flora in that area cannot survive in that area without light and animals living in that area will not get the food and the plants and animals will perish and the ecosystem cannot survive.

(d) Cattle go to ponds for drinking water, so they are a constituent of pond ecosystem (F)
Cattles likes tigers, lions, cows, deers, buffaloes, go to take water from the pond and return to their dwellings as tigers, deers etc. come to the forest so they form a forest ecosystem. But plants like hydrilla, vallineria, lotus etc. and animals like frogs, beetles, fish live in the pond and form the pond ecosystem. But animals like buffalo which come only to take~water cannot form a part of the pond ecosystem.

2. Match the items in Column I with as many items as possible in Column II.
Selina Concise Biology Class 8 ICSE Solutions – Ecosystems 1
Selina Concise Biology Class 8 ICSE Solutions – Ecosystems 2
Answer:

Selina Concise Biology Class 8 ICSE Solutions – Ecosystems 3
3. Rewrite the following in their correct sequence in a food chain:
(a) Snake → Grasshopper → Grass → Frog
(b) Grass → Tiger → Deer
(c) Snake → Peacock → Rat → Wheat

Answer:

(a) Grass → Grasshopper → Frog → Snake
(b) Grass → Deer → Tiger
(c) Wheat → Rat → Snake → Peacock

Long Answer Type:

Question 1.
Differentiate among primary, secondary and tertiary consumers. Give one example of each in a food chain.
Answer:
All plants produce food through photosynthesis and are categorised as self food producers i.e. these are autotrophs. There are plant eating animals called herbivores as Rabbits, deers, pigeons, cows, buffaloes etc. and insects like grasshoppers, bees, butterflies and crickets also eat plants or plant products as fruits, flowers, pollen grains and plant juices. Such animals are called primary consumers.
Animals like tigers, lions, wolves, lizards, frogs eat the primary consumers. Birds vultures, kites, eagles eat the primary consumer, (i.e. These birds are well eat the flesh of many birds like pigeons, sparrows.) These animals or birds are called secondary consumers.
Animals like snakes are eaten by the peacocks, they eat the secondary consumers and are called tertiary consumers.
Owls, eagle are top carnivore. So it is quaternary consumer.

Question 2.
Define the term (a) flora and (b) fauna.
Answer:
Flora: Plants occurring in a particular is called flora of that area i.e. vegetative growth forms flora. Flora deals with plants.
Fauna: The animals occurring in a area form the fauna of that area. Fauna deals with animals.
Flora and fauna of an area is the plants and animals found in that area.

Question 3.
List any three members each of the flora and fauna of tropical rain forests.
Answer:
Tropical rain forest are on western coast of India and in the north, east.
Flora: bamboos, ferns, shrubs (Evergreen trees).
Fauna: leopards, jungle cats, monkeys, snakes, flying squirrels, insects, snails, centipedes, millipedes.

Question 4.
Define the following terms and give two examples in each case.
(a) Symbiosis
(b) Parasitism
(c) Predation
Answer:
(a) Symbiosis: It refers to relationships between organisms of different species that show on intimate association with each other. Symbiotic relationships provide atleast one of the participating species with a nutritional advantage.
Examples of Symbiosis Relationships are of Fungus and photosynthestic alga and Microbes and cattle.

(b) Parasitism: Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Examples of Parasitism are 4 tapeworms, flukes, the plasmodium species and mosquitoes.

(c) Predation: A predator is any consumer that kills and eats another living organism in order to obtain energy. The organism being eaten is called the prey.
Examples are Lions, Deer, Wolves, Eagles.

Selina Concise Chemistry Class 7 ICSE Solutions – Physical and Chemical Changes

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Selina Concise Chemistry Class 7 ICSE Solutions – Physical and Chemical Changes

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 7 Chemistry. You can download the Selina Concise Chemistry ICSE Solutions for Class 7 with Free PDF download option. Selina Publishers Concise Chemistry for Class 7 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 7 Chemistry Chapter 2 Physical and Chemical Changes

Points to Remember :

  1. All changes are classified into two types
    (i) Physical change
    (ii) Chemical change.
  2. Physical Change— A physical change is a temporary change in which no new substance is formed and chemical composition remains same. e.g. Melting of ice.
  3. Chemical Change— A chemical change is a permanent change, in which a new substances are formed whose chemical composition and physical properties are different, e.g. Burning of a candle.
  4. Chemical Reaction— Any chemical change in matter involving its transformation into one or more new substances is called a chemical reaction.
  5. Chemical Equations— A chemical equation is the symbolic representation of a chemical reaction using the symbols and the formulae of the substances involved in the reaction.
  6. The substances that react with one another are called reactants, and the new substances thus formed are called products.
  7. A balanced chemical reaction is one in which the number of the atoms of each element on the
  8. reactant side is equal to the number of atoms of that element on the product side.
  9. The law of conservation of mass states that mass can neither be created nor be destroyed.
  10. A chemical equation gives both qualitative and quantitative information about reactants aftd products.
  11. The type of chemical reaction in which two substances combine to form a new substance is known as combination reaction.
  12. The type of chemical reaction in which a substance breaks up on heating to form two or more simpler substances,
    which can be either elements or compounds, known as decomposition reaction.

Exercise

Question 1.
(a) Define:
(i) a physical change
(ii) a chemical change
(b) Give two examples for each of the above two changes.
Answer:
(a) (i) Physical chagne : A temporary change in which no new substance is formed, the composition of substance remains the same, though its state, shape and size may change.
(ii) Chemical change : A permanent change in which new substances are formed whose composition and properties are completely different from those of the original substances.
(b) Physical change:
(i) Change of water into its vapours.
(ii) Heating of iron rod.
Chemical change:
(i) Burning of wood.
(ii) Breathing.

Question 2.
What are reversible and irreversible changes ? Give one example for each.
Answer:

  1. Reversible change : When a change in a substance can be reversed by changing the conditions, it is said to be a reversible change.
    Example : Melting of ghee or wax.
  2. Irreversible change : When a substance can not be brought back to its original state after a change, it is said to be an irreversible change.
    Example : Souring of milk.

Question 3.
Mention a change which is always
Answer:

  1. Desirable : Changes that are useful to man are desirable changes, e.g. change of milk into curd.
  2. Undesirable : Change that brings about destruction is an undesirable change, e.g. floods and epidemics are undesirable changes.
  3. Periodic : Changes that are repeated at regular intervals of time are called periodic changes, e.g. change of day and night.

Question 4.
Is burning a physical change or a chemical change? Why?
Answer:
Burning is a chemical change as new substance is formed with new properties and it cannot be reversed.

Question 5.
A burning candle shows both physical and chemical changes. Explain ?
Answer:
A burning candle produces wax vapours which solidify and form wax again is physical change. At the same time wax on burning produces water vapours and carbondioxide which escape into the atmosphere which are new substances with new properties. It is a chemical change.
Hence burning of candle shows both physical and chemcial changes.

Question 6.
State three differences between evaporation and boiling
Answer:

EvaporationBoiling
  1. Evaporation is a slow process.
  2. Evaporation takes place from the surface of the liquid.
  3. Evaporation takes place at all temperature.
  1. Boiling is a fast process.
  2. Bgiling takes place from all parts of the liquid.
  3. Boiling takes place at a fixed temperature on heating.

Question 7.
State four differences between physical and chemical changes.
Answer:
Four differences are :

Physical changeChemical change
  1. No new substances with new properties are formed.
  2. It can be reversed by simple physical methods.
  3. It is temporary change.
  4. Energy is neither needed nor produced.
  1. New substances with new properties are formed.
  2. Change cannot be reversed by simple physical methods.
  3. It is permanent change.
  4. Energy is either needed or evolved.

Question 8.
What do you observe when :

  1. water is boiled
    On boiling water changes into steam (gas) physical change.
  2. a piece of paper is burnt
    On burning piece of paper produces carbon dioxide and ash is left behind. Is a chemical change.
  3. some ice cubes are kept in a glass tumbler
    Ice cubes (solid) turn into water (liquid) only state changes (physical change).
  4. solid ammonium chloride is heated
    Solid ammonium chloride on heating changes into vapours (change of state) is physical change.
  5. an iron nail is kept in tap water for few days
    We observe reddish brown coating on the nail called rust (entirely new substance) is chemical change.
  6. a spoon of sugar is heated in a pan
    When a spoon of sugar is heated in a pan, black (charred sugar) (carbon) is seen. Is a chemical change.
  7. lighted match stick is brought near the mouth of the test tube containing hydrogen gas.
    We observe that hydrogen bums at the mouth of test tube with blue flame and pop sound is heard. It is chemical change.
  8. quick lime is dissolved in water.
    The following two observations will be observed
    (i) A hissing sound is observed.
    (ii) The mixture starts boiling and lime water is obtained.
  9.  liittle ammount of curd is added to a bowl containing warm milk and kept for five hours.
    When a little amount curd is added to a bowl containing warm milk and kept for five hours, a permanent change occured.
    The milk will change to curd. On boiling water changes into steam (gas) physical change.

Question 9.
Name a chemical change which takes place in presence of:
Answer:
Heat:

  1. Burning of paper.
  2. Cooking of food need heat.

Light :

  1. Formation of food by plants i.e. photosynthesis need light.
  2. Hydrogen and chlorine react in presence of light

Electricity:

  1. Water breaks into hydrogen and oxygen on passing electricity.
  2. Sodium chloride solution breaks up into its components sodium and Chlorine on passing electric current through sodium chloride solution.

Objective Type Questions

Question 1.
Fill in the blanks.

  1. A new substance is always formed in a chemical change.
  2. Melting of ice is a physical change.
  3. When a candle burns, wax melts. Melting of wax is a physical change.
  4. Chemical change occurs as a result of rearrangement of atoms between two substances.
  5. Burning of a fuel is a chemical change.
  6. Revolution of the earth around the sun is a natural periodic change.
  7. Growing of a seedling into a plant is chemical change.

Question 2.
State whether the following are physical or chemical changes.

  1. glowing of a bulb — physical change,
  2. burning of sugar — chemical change,
  3. heating of water — physical change,
  4. growing of a piglet into a pig — chemical change,
  5. burning of wood — chemical change,
  6. passing electric current through a heater rod — physical change.
  7. water cycle in nature — physical change,
  8. respiration in living beings — chemical change,
  9. shaping a piece of glass — physical change,
  10. lightning — chemical change,
  11. (energy produced) dissolving sugar in water — physical change,
  12. heating a mixture of iron filings and sulphur—chemical change.
  13. mixing oil with water — physical change.
  14. cutting wood into small pieces — physical change,
  15. photosynthesis — chemical change.
  16. Digestion of food — chemical change.
  17. Melting of wax — physical change.
  18. Boiling of an egg — chemical change.
  19. Slaking of lime — chemical change.

Question 3.
Match the following:

Physical and Chemical changes 1
Physical and Chemical changes 3
Answer:
Physical and Chemical changes 4

Question 4.
Write true or false against the following statements :

  1. Cutting of paper into pieces is a chemical change.
    False
  2. Rusting of iron is a chemical change.
    True
  3. Earthquake is a desirable change.
    False
  4. Melting of ice is a physical change.
    True
  5. Burning of sugar is a temporary change.
    False

Multiple Choice Questions

Tick (√) the correct alternative from the choice given for the following statements :
Question 1.
A substance which can not sublime is
Answer:

  1. iodine
  2. camphor
  3. sugar
  4. dry ice

Question 2.
When you put some ice cubes in a glass, droplets of water are formed on the outerwall of the glass. This explains the phenomenon of
Answer:

  1. melting
  2. freezing
  3. condensation
  4. evaporation

Question 3.
Burning is a
Answer:

  1. slow process
  2. fast process
  3. natural process
  4. none of the above

Question 4.
Which one of the following is volatile in nature ?
Answer:

  1. common salt
  2. petrol
  3. water
  4. milk

Question 5.
An example of both physical and chemical change is
Answer:

  1. burning of candle
  2. melting of ice
  3. cooking of food
  4. blowing of bulb

Question 6.
The compound rust is a hydrated oxide of
Answer:

  1. copper
  2. aluminium
  3. iron
  4. gold

Question 7.
When sugar is heated, its colour changes into
Answer:

  1. red
  2. brown
  3. black
  4. grey

Question 8.
A pop sound is heard when a lighted match stick is brought
near the mouth of a jar. This indicates the release of gas.
Answer:

  1. oxygen
  2. hydrogen
  3. nitrogen
  4. water-vapour

Question 9.
When we add water to the following substances, which one will show a chemical change ?
Answer:

  1. salt
  2. sugar
  3. oild
  4. quick lime

Selina Concise Physics Class 7 ICSE Solutions – Heat

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Selina Concise Physics Class 7 ICSE Solutions – Heat

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.

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Selina Concise ICSE Solutions for Class 7 Physics Chapter 5 Heat

  • Points to Remember
  •  Heat is a form of energy that leads to the sensations of hotness or coldness.
  •  Temperature is the degree of hotness and coldness of a body.
  •  Thermometer is used to measure temperature.
  •  The S.I. unit of temperature is °C.
  •  The most common liquid for a thermometer is mercury.
  •  The main sources of heat are (i) Fire (ii) Sun (iii) Electricity.
  •  Those substances which can easily catch fire are called inflammable substances.
  •  Those substances which are fire resistant are called non-inflammable substances.
  •  The fixed temperature at which freezing of liquid occurs is known as freezing point.
  •  The temperature at which vapourisation occurs is known as the boiling point.
  •  Substances through which heat is easily conducted are called good conductors e.g. silver, gold, copper etc.
  •  Substances through which heat is not easily conducted are called Insultors.
  •  Radiation is the process of transfer of heat from a hot body to a cold body without affecting the intermediate medium.

Test Yourself

A. Objective Questions 

1. Write true or false for each statement

(a) On touching a lump of ice, we feel cold because some heat passes from our body to the ice.
Answer. True.

(b) Heat flows from a body at a high temperature to a body at a low temperature when they are kept in contact. .
Answer. True.

(c) All solids expand by the same amount when heated to the same rise in temperature.
Answer. False.

(d) Telephone wires are kept tight between the two poles in summer.
Answer. False.

(e) Equal volumes of different liquids expand by different amounts when they are heated to the same rise in temperature.
Answer. True.

(f) Solids expand the least and gases expand the most on being heated.
Answer. True.

(g) A mercury thermometer makes use of the property of expansion of liquids on heating.
Answer. True.

(h) Kerosene contracts on heating.
Answer. False.

(i) Water is a bad conductor of heat.
Answer. True.

(j) Medium is necessary for the transfer of heat by radiation.
Answer. False.

(k) Land and sea breezes are convection currents of cold and warm air.
Answer. True.

(l) Liquids are heated by conduction and radiation.
Answer. False.

(m) Black surfaces are the poor absorbers of heat radiations.
Answer. False.

2. Fill in the blanks

(a) Heat is a form of energy.
(b) Temperature determines the degree of hotness or coldness of a body.
(c) On heating a body, its temperature rises.
(d) We use a thermometer for measuring the temperature of a body.
(e) The S.I. unit of temperature is kelvin.
(f) In a thermometer, the commonly used liquid is mercury.
(g) The temperature of a normal human body is 37 °C.
(h) A person is said to have fever if his body temperature is more than 98.6
(i) A hot metallic piece is placed in tap water contained in a bucket. Heat will flow from metallic piece to water.
(j) The temperature of boiling water is 100°C.
(k) Liquids expand more than the solids.
(l) Gases expand more than the liquids.
(m) Heat transfer in solids is by conduction.
(n) Heat transfer in liquids and gases is by convection.
(o)Metals are conductors of heat.
(p) Still air is an insulator of heat.
(q) Black and dull surfaces are good absorbers of heat.

3. Match the following

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 1

4. Select the correct alternative

(a) If we add a lump of ice to a tumbler containing water,

  1. heat flows from water to ice
  2.  heat flows from ice to water
  3.  heat flows from water to ice if water is more
  4.  heat flows from ice to water if ice is more

(b) The temperature of pure melting ice is

  1.  0°C
  2.  100°C
  3.  95°C
  4.  98.6°F

(c) A thermometer uses

  1.  water
  2. mercury
  3.  air
  4.  none of the above

(d) Which of the statement is correct

  1.  Iron rims are cooled before they are placed on cart wheels
  2.  A glass stopper gets tight on warming the neck of the bottle
  3.  Telephone wires sag in winter, but become tight in summer
  4. A little space is left between two rails on a railway track

(e) Heat in a liquid is transferred by

  1.  conduction
  2. convection
  3.  radiation
  4.  conduction and radiation

(f) In the process of convection, heat travels

  1.  sideways
  2.  downwards
  3. upwards
  4.  in all directions

(g) The vacuum kept in between the walls of a thermos flask reduces the heat transfer by

  1.  conduction only
  2.  convection only
  3.  radiation only
  4. conduction and convection

B. Short/Long Answer Questions

Question 1.
What is heat ? State its S.I. unit.
Answer:
Heat is a form of energy which flows. It is the energy of motion of molecules constituting the body.
The unit of heat is same as that of energy, The S.I. unit of heat is joule (abbreviated as J) and other common units of heat are calorie and kilo calorie, where 1 k cal = 1000 cal.

Question 2.
What is meant by the term temperature.
Answer:
Temperature is a quantity which tells the thermal state of a body (i.e. the degree of hotness or coldness). It determines the direction of flow of heat when the two bodies at different temperatures are placed in contact.

Question 3.
State the three units of temperature.
Answer:
The S.I. unit of temperature is kelvin or K. The other most common unit of temperature is degree Celsius (°C) and degree Fahrenheit (°F).

Question 4.
Name the instrument used to measure the temperature of a body.
Answer:
To measure the temperature of a body with the help of a thermometer.

Question 5.
Name two scales of temperature. How are they inter-related?
Answer:
Two scales of temperature are
(i) Celsius (ii) Fahrenheit
Relation:

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 2

Question 6.
How is the size of a degree defined on a Celsius scale ?
Answer:
The interval between the ice point and steam point divided by 100 (hundred) equal parts is called a degree on the Celsius scale.

Question 7.
How is the size of a degree defined on a Fahrenheit scale?
Answer:
The interval between the ice point and steam point divided into 180 equal parts is called a degree on the Fahrenheit scale.

Question 8.
State the temperature of (i) ice point and (ii) steam point, on the Celsius scale.
Answer:
(i) Ice point. Is the the mark on Celsius scale at which ice melts. Ice point on the Celsius scale is 0°C.
(ii) Steam point. On the Celsius scale is the mark at which water changes into steam at normal atmospheric pressure. On Celsius scale it is 100°C.

Question 9.
Write down the temperature of (i) lower fixed point, and (ii) upper fixed point, on the Fahrenheit scale.
Answer:
Lower fixed point: On the Falirenheit scale is the mark at which pure ice melts. It is 32°F on Fahrenheit scale.
Upper fixed point: On the Fahrenheit scale is the mark at which water starts changing into steam at normal atmospheric pressure. It is 212°F.

Question 10.
What is the Celsius scale of temperature ?
Answer:
Celsius scale is that which has ice point as 0°C and steam point marked as 100°C.

Question 11.
What is the Fahrenheit scale of temperature ?
Answer:
Fahrenheit scale is that which has ice point as 32°F and the steam point marked as 100°C.

Question 12.
What is the Kelvin scale of temperature ?
Answer:
On Kelvin scale of temperature zero mark is when no molecular motion occurs. Ice point is at 273 and steam point is at 373 K. Thus 0 K = – 273°C and one degree on Kelvin scale is same as one degree on Celsius scale.

Question 13.
The fig. shows a glass tumbler containing hot milk which is placed in a tub of cold water. State the direction in which heat will flow.

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 3
Answer:
When we bring two objects of different temperature together, energy will always be transferred from hotter to the cooler object.
Here, also heat will flow from hot milk tumbler to tub of cold water.

Question 14.
Draw a neat labelled diagram of a laboratory thermometer.
Answer:

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 4

Question 15.
Write down the body temperature of a healthy person.
Answer:
The temperature of a healthy persons is 98.6 degrees fahrenheit or 37.0 degree Celsius or 310 k.

Question 16.
What do you understand by thermal expansion of a substance ?
Answer:
The expansion of a substance when, heated, is called thermal expansion.
Or
Thermal expansion is the tendency of matter to change .in shape, area and volume in response to a change in temperature.

Question 17.
Name two substances which expand on heating.
Answer:
Mercury and Aluminium wire.

Question 18.
Why do telephone wires sag in summer ?
Answer:
The telephone wires will sag in summer due to expansions and will break in winter due to contraction.
Therefore, while putting up the wires between the poles, care is taken that in summer they are kept slightly loose so that they may not break in winter due to contraction.
While in winter they are kept light so that they may not sag too much in summer due to expansion.

Question 19.
Iron rims are heated before they are fixed on the wooden wheels. Explain the reason.
Answer:
The wooden wheels of a bullock-cart are fitted with iron tyres. To ensure a tight fit, the tyre is made slightly smaller in diameter than the wheel. The tyre is first heated due to which it expands. The heated tyre is then fitted on the wheel. When the tyre cools, it contracts and makes a tight fit on the wheel.

Question 20.
Why are gaps left between successive rails on a railway track ?
Answer:
The rails of railway track are made of steel. While laying the railway track, a small gap is left between the two successive length of rails. The reason is that the rails expand in summer. The gap is provided to allow for this expansion. If no gap is left, the expansion in summer will cause the rails to bend sideways. This may result in a train accidents.

Question 21.
A glass stopper stuck in the neck of a bottle can be removed by pouring hot water on the neck of the bottle. Explain why ?
Answer:
When hot water is poured over the neck of the bottle, it expands. As a result the stopper gets loosened and can be removed easily.

Question 22.
Why is a cement floor laid in small pieces with gaps in between?
Answer:
The floor is laid in small pieces with gaps in between to allow for the expansion during summer. However glass strips can be placed in the gaps.

Question 23.
One end of a steel girder in a bridge is not fixed, but is kept on roliers. Give the reason.
Answer:
In the construction of a bridge, steel girders are used. One end of the girder is fixed into the concrete or brick pillars and its other end is not fixed, but it is placed on rollers. The reason is that if there is any rise (or fall) in temperature of atmosphere, the girder can freely expand (or contract) without affecting the pillars.

Question 24.
Describe one experiment to show that liquids expand on heating.
Answer:
(i) Take an empty bottle with a tight fitting cork having a hole drilled in its middle, a drinking straw, two bricks, a wire guaze and a burner.
(ii) Fill the bottle completely with water and add few drops of ink in it to make it coloured.
(iii) Fix the cork in the mouth of the bottle and pass the drinking straw through the cork. Put some molten wax around the hole so as to avoid the leakage of water.
(iv) Pour some more water into the drinking straw so that water level in the straw can be seen. Mark the water level in the straw as shown in Figure.

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 5
(v) Place the bottle on the wire gauze kept over the two bricks as shown in Figure. Then heat the bottle by means of a burner.
(vi) Look at the level of water in the straw.
You will notice that as the water is heated more and more, the level of water in the drinking straw rises. This shows that water expands on heating.

Question 25.
State one application of thermal expansion of liquids.
Answer:
Mercury is a metal found in liquid state. It expands more and uniformly over a wide range of temperature. So mercury is used as thermometric liquid.

Question 26.
Describe an experiment to show that air expands on heating.
Answer:
(i) Take an empty bottle. Actually the empty bottle contains air. Attach a rubber balloon to its neck as shown in Figure. Initially, the balloon is deflated.
(ii) Place the bottle in a water bath containing boiling water. After some time you will notice that the balloon gets inflated as shown in Figure. The reason is that the air inside the bottle expands on heating and it fills the balloon.

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 6
(iii) Take the bottle out of the water bath and 7 allow it to cool by itself. We will notice that the balloon gets deflated and it collapses. This is because the air inside the balloon and the bottle, has contracted on cooling. The air from balloon passes to the bottle, so the balloon gets deflated.

Question 27.
An empty glass bottle is fitted with a narrow tube at its mouth. The open end of the tube is kept in a beaker containing water. When the bottle is heated, bubbles of air are seen escaping into the water. Explain the reason.
Answer:
When the bottle is heated, bubbles of air are seen escaping into the water. This happens because the air present in glass bottle expands on heating and tries to escape out through the tube into the water.

Question 28.
State which expands more, when heated to the same temperature : solid, liquid or gas ?
Answer:
Gases expand much more than the liquids and the solids. Like liquids, the gases do not have a definite shape, so they also have only the cubical expansion.

Question 29.
Name the three modes of transfer of heat.
Answer:
There are three modes of transfer of heat (i) Conduction (ii) Convection (iii) Radiation.
(i) Conduction “is that mode of transfer of heat, when heat travels from hot end to cold end from particle to particle of the medium, without actual movement of particles.”
(ii) Convection. “Is a process of transfer of heat by actual move-ment of the medium particles.”
(iii) Radiation. “Is that mode of transfer of heat in which heat directly passes from one body to the other body without heating the medium.”

Question 30.
Name the mode of transfer of heat in the following :
(a) solid,
(b) liquid,
(c) gas
(d) vacuum
Answer:

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 7

Question 31.
What are the good and bad conductors of heat ? Give two examples of each.
Answer:
Good conductors. “The substances through which heat is easily conducted are called good conductors of heat.”
Example : Copper, iron.
Bad conductors. “The substances through which heat is not conducted easily are called bad conductors of heat or poor conductors of heat.”
Example : Wood, cloth.

Question 32.
Name a liquid which is a good conductor of heat.
Answer:
Mercury is good conductor of heat.

Question 33.
Name a solid which is a good conductor of heat.
Answer:
Aluminium is a good conductor of heat.

Question 34.
Select good and bad conductors of heat from the following :
copper, mercury, wood, iron, air, saw-dust, cardboard, silver, plastic, wool.
Answer:
Good conductors — Mercury, copper, silver, iron.
Bad conductors — Wood, air, saw dust, plastic, wool, cardboard.

Question 35.
Why is an oven made of double walls with the space in between filled with cork ?
Answer:
An oven is made of double walls and the space between them is filled with wool, cork etc. because the wool and cork are the insulator of heat. They prevent the heat of the oven to escape.

Question 36.
Why do we use cooking utensils made up of copper.
Answer:
Cooking utensils are made of metals such as copper, aluminium, brass, steel etc., so that heat is easily conducted through the base to their contents. But they are provided with handles of bad conductors (such as ebonite or wood) to hold them easily as handles will not conduct heat from the utensil to our hand.

Question 37.
Why is a tea kettle provided with an ebonite handle ?
Answer:
Tea kettles are provided with wooden or ebonite handles. The wood or the ebonite being the insulators of heat, does not pass heat from the utensils to our hand. Thus, we can hold the hot utensils or pans comfortably by their handles.

Question 38.
In summer, ice is kept wrapped in a gunny bag. Explain the reason.
Answer:
In summer, the ice is kept wrapped in a gunny bag or it is covered with saw dust. The air filled in the fine pores of the gunny bag or saw dust, is the insulator of heat. The air does not allow heat from outside to pass through it to the ice. Thus, the ice is prevented from melting rapidly.

Question 39.
Explain why
(a) we wear woolen clothes in winter.
(b) the water pipes are covered with cotton during very cold weather.
Answer:
(a) Woolen clothes have fine pores filled with air. Wool and air both are bad conductors of heat. Therefore in winter, we wear woolen clothes as they check the conduction of heat from the body to the surroundings and thus keeps the body warm.
(b) During very cold weather, the water pipes are covered with cotton. The cotton has air trapped in its fine pores. The cotton and air are the insulators of heat. They do not pass heat from water inside the pipes to the outside atmosphere. Thus, cotton prevents the water in the pipes from freezing.

Question 40.
Why are quilts filled with fluffy cotton ?
Answer:
Quilts are filled with fluffy cotton. Air is trapped in the fine pores of cotton. Cotton and air are the insulators of heat. They check heat from our body to escape and thus keep us warm.
The newly made quilts are warmer than the old ones because in the old quilts, there is no air trapped in the cotton.

Question 41.
State the direction of heat transfer by way of convection.
Answer:
By the process of convection, heat is always transferred vertically upwards. The reason is that the medium particles near the source of heat absorb heat from the source and they start moving faster. As a result, the medium at this place becomes less dense so it rises up and the medium from above being denser, moves down to take its place. Thus, current is set up in the medium which is called a convection current. The current continues till the entire medium acquires the same temperature.

Question 42.
Why is a ventilator provided in a room ?
Answer:
Ventilators and windows are provided in rooms for proper ventilation. The reason is that when we breathe out in a room, the air in the room becomes warm and impure. The warm air is less dense i.e. lighter, so it rises up and moves out through the ventilators. Then the cold fresh air comes in the room through the windows to take its place. Thus the continuous circulation of fresh air keeps the air in the room fresh.

Question 43.
Why are chimneys provided over furnace in factories ?
Answer:
Chimneys are provided over the furnace in factories. This is because the hot gases coming out of the furnace are less dense than the air. They rise up through the chimney. The smoke, fumes etc. around the furnace rush in so as to take their place and they are sucked out. Thus, the chimney helps to remove the undesired fumes, smoke etc. from the premises.

Question 44.
What are the land and sea breezes ? Explain their formation.
Answer:
LAND BREEZE : Blowing of breeze (air) from land towards sea is called land breeze.
During night land and sea water both lose heat. Specific heat capacity of land being very low as compared to that of sea water, land loses heat energy fast and cools more rapidly as compared to sea. Sea water being at higher temperature, the air above it becomes lighter and rise up. Air from land being at higher pressure. So air from land starts blowing towards sea and gives rise to Land Breeze.

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 8
SEA BREEZE : Blowing of breeze (cold air) from sea towards land during the day is called the SEA BREEZE. During day time land and sea both are heated equally by the sun, but land has very low specific heat capacity as compared to sea, is heated up more quickly. Thus air above land due to heat becomes lighter and rises up. Thus pressure decreases and cold and humid air above the sea starts blowing towards land, thereby giving rise to SEABREEZE.

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 9

Question 45.
Why is the freezing chest in a refrigerator fitted near its top?
Answer:
Freezing chest in a refrigerator is fitted near the top, because it cools the remaining space of the refrigerator by convection current. Air near the top comes in contact with the freezing chest gets cooled, becomes denser and therefore descends while the hot air from the lower part rises and hence convection currents produced cool the whole space inside.

Question 46.
Explain briefly the process of heat transfer by radiation.
Answer:
RADIATION. “The transfer of heat energy from a hot body to cold body directly, without heating the medium between two bodies is called RADIATION.”
The radiant heat or thermal radiation is of the form of ELECTROMAGNETIC WAVES. These waves can travel even in vacuum in all directions in straight line with the speed of light. They do not heat the medium through which they pass. Heat radiations are also called INFRA-RED RADIATIONS because the wavelength of heat radiations is longer than that of visible light. These radiations can cause heating effect only if they are absorbed by some material.

Question 47.
Give one example of heat transfer by radiation.
Answer:
When we sit in the sun, we feel warm. We cannot get heat from the sun by the process of conduction or convection because most of the space between the sun and the earth is a vacuum and both of these modes of heat transfer require medium. Hence, one must be getting heat from the sun by the mode of radiation.

Question 48.
Why do we prefer to wear white or light coloured clothes in summer and black or dark coloured clothes in winter ?
Answer:
We prefer to wear white clothes in summer. The reason is that the white clothes reflects most of the sun’s heat and absorb very little of the sun’s heat, thus they keep our body cool.
We prefer to wear black and dark coloured clothes in winter. The reason is that the black or dark colour clothes absorb most of the sun’s heat and keep our body warm.

Question 49.
The bottom of a cooking utensil is painted black. Give the reason.
Answer:
The bottom part of the cooking utensil or pan is painted black. The reason is that the black surface absorbs more heat and so the contents of utensil or pan get cooked rapidly if its bottom part is painted black.

Question 50.
Draw a labelled diagram of a thermo flask. Explain how the transfer of heat by conduction, convection and radiation is reduced to a minimum in it.
Answer:
Heat transfer is minimised because of:
(1) The vacuum between the two walls, rubber, glass, cork and air do not allow the loss of heat by conduction.
(2) Cork in the neck of flask and the cup over it prevent loss of heat by convection.
(3) Heat cannot be lost by conduction or convection because of vacuum between the two walls.
(4) Heat loss is also minimised by radiation, by making outer surface of inner wall and inner surface of outer wall silvered. The inner wall is a BAD RADIATOR and the outer wall is a GOOD REFLECTOR of radiation.

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 10

C. Numericals

Question 1.
The temperature of a body rises by 1°C. What is the corresponding rise on the (a) Fahrenheit scale (b) Kelvin scale?
Answer:
(a) Since 100 divisions on Celsius scale =180 divisions on the Fahrenheit scale 1 division on Celsius scale
∴ 1 division on Celsius scale
= 1.80 / 1.00 × 1
= 1.8 divisions in the Fahrenheit scale.
For 1°C rise corresponding rise in Fahrenheit = 1.8°F
(b) Since 100 divisions in the Celsius scale = 100 divisions in the Kelvin scale
1 division on Celsius scale = 100 / 100 × 1
= 1 division on Kelvin scale
For 1°C rise corresponding rise in Kelvin is 1 K.

Question 2.
The temperature rises by 18°F. What is the rise on the Celsius scale ?
Answer:
Since 100 divisions on the Celsius scale =180 divisions on the Fahrenheit scale
∴ 18 divisions on Fahrenheit scale.

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 11

Question 3.
Convert 5°F to the Celsius scale.
Answer:

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 12

Question 4.
Convert 40°C to the (a) Fahrenheit scale (b) Kelvin Scale.
Answer:
(a) Fahrenheit scale
C = 40°C
Substitute value of C = 40° in below equation

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 13

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 14

Question 5.
Convert – 40°F to the Celsius scale.
Answer:

Selina Concise Physics Class 7 ICSE Solutions Chapter 5 Heat 15

Selina Concise Physics Class 7 ICSE Solutions – Motion

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Selina Concise Physics Class 7 ICSE Solutions – Motion

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 2 Motion

  • Points to Remember
  •  Motion— Motion is the change in position with respect to a set of stationary landmarks.
  •  Types of motion are translatory, rotatory and oscillatory.
  •  A body is said to move in a translatory motion if the whole body moves through the same distance in the same interval of time.
  •  A body is said to be in rotatory motion if it moves about a fixed point without changing the radius of its motion.
  •  A body is said to be in oscillatory motion if it moves to and fro about its mean position.
  •  A body is said to be in vibratory motion if the body moves to and fro in a particular style.
  •  Oscillation of pendulum is one complete to and fro motion.
  •  The maximum displacement on either side of a mean position is called amplitude.
  •  A motion which repeats itself at regular intervals of time is called periodic motion.
  •  A physical quantity which has only magnitude and no direction is called a scalar quantity.
  •  A physical quantity which has magnitude as well as direction is called a vector quantity.
  •  Speed is the distance travelled per unit time. It is a scalar quantity.
  •  The displacement per unit time is known as the velocity of the body. It is a vector quantity.
  •  The rate of change of velocity is called acceleration. It is a vector quantity.
  •  Frequency is the number of complete oscillations in one second.
  •  Unit of frequency is Hertz.
  •  Motion is of two types (a) uniform (b) non-uniform motion.

Test yourself

A. Objective Questions

1. Write true or false for each statement

(a) Two trains going in opposite directions with the same speed are at rest relative to each other.
Answer. False.

(b) A ball is thrown vertically upwards. Its motion is uniform throughout.
Answer. False.

(c) The motion of a train starting from one station and reaching at another station is non-uniform.
Answer. True.

(d) A motion which repeats itself after a fixed interval of time is called periodic motion.
Answer. True.

(e) A ball thrown by a boy from a roof-top has oscillatory motion.
Answer. False.

(f) Mass has both magnitude and direction.
Answer. False.

(g) .Weight always acts vertically downwards.
Answer. True

(h) Mass varies from place to place but weight does not.
Answer. False

2. Fill in the blanks

(a) Two boys cycling on the road with the same speed are at rest relative to each other.
(b) The motion in a straight line is rectilinear motion.
(c) One to and fro motion of a clock pendulum takes time = 2 s
(d) 36 km h-1 = 10 m s-1
(e) Total distance travelled = average speed × total time taken.
(f) The weight of a girl is 36 kgf. Her mass will be 36 kg.
(g) The weight of a body is measured using a spring balance.

Activity

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 1

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 2

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 3

3. Match the following

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 4

4. Select the correct alternative

(a) A book lying on a table is an example of

  1.  a body at rest
  2.  a body in motion
  3.  a body neither at rest nor in motion
  4.  none of these

(b) The motion of a pendulum is

  1.  rotatory
  2. oscillatory
  3.  curvilinear
  4.  rectilinear

(c) A car moving on a straight road is an example of

  1.  rotatory motion
  2.  rectilinear motion
  3.  oscillatory motion
  4.  periodic motion

(d) A ball falls down vertically. Its motion is

  1.  periodic
  2.  linear
  3.  circular
  4.  vibratory

(e) If a body covers equal distance in equal interval of time, the motion is said to be

  1.  uniform
  2.  non-uniform
  3.  oscillatory
  4.   rotatory

(f) A boy goes from his house to school by bus at a speed of 20 km h-1 and returns back through the same route at a speed of 30 km h_1. The average speed of his journey is

  1.  24 km h-1
  2.  25 km h-1
  3.  30 km h-1
  4.  20 km h-1

(g) The earth attracts a body of mass 1 kg with a force of 10 N. The mass of a boy is 50 kg. His weight will be

  1.  50 kg
  2.  500 N
  3.  50 N
  4.  5 N

B. Short/Long Answer Questions

Question 1.
Explain the meaning of the terms rest and motion.
Answer:
Rest— A body is said to be at rest if it does not change its position with respect to its immediate surroundings.
Motion— A body is said to be in motion if it changes its position with respect to its immediate surroundings.

Question 2.
Comment on the statement ‘rest and motion are relative terms’. Give an example.
Answer:
Imagine you are sitting inside a moving bus. When you look outside you will observe that you are moving. Now look to the roof of the bus. With respect to the roof of bus, you are at rest. Hence it is concluded that rest and motion are relative terms.

Question 3.
Fill in the blanks using one of the words : at rest, in motion.
(a) A person walking in a compartment of a stationary train is relative to the compartment and is relative to the platform.
(b) A person sitting in a compartment of a moving train is relative to the other person sitting by his side and is relative to the platform.
Answer:
(a) A person walking in a compartment of a stationary train is in motion relative to the compartment and is in motion relative to the platform.
(b) A person sitting in a compartment of a moving train is at rest . relative to the other person sitting by his side and is in motion relative to the platform.

Question 4.
Name five different types of motion you know.
Answer:
The different types of motion are :
1. Translatory motion
2. Rotatory motion
3. Oscillatory motion
4. Vibratory motion
5. Periodic motion
6. Multiple motion
7. Random motion.

Question 5.
What do you mean by translatory motion ? Give one example.
Answer:
If an object like a vehicle, moves in a line in such a way that every point of the object moves through the same distance in the same time, then the motion of the object is called translatory motion.
Example :
The motion of an apple falling from a tree, the motion of a man walking on a road, the motion of a box when pushed from one comer of a room to the other, are all the translatory motion.

Question 6.
Explain the meanings of (i) rectilinear motion, and (ii) curvilinear motion. Give one example of each.
Answer:
(i) Rectilinear motion — If the motion of a body is along a straight line, it is said to be the rectilinear or linear motion. The motion of bullet fired from a gun.
(ii) Curvilinear motion — If the motion of a body is along a curved path, it is said to be the curvilinear motion. For example, the motion of a cycle while taking a turn on the road, a car moving along a curved path, a ball thrown by an athlete are in curvilinear motion.

Question 7.
What is rotatory motion ? Give two examples.
Answer:
Rotatory motion— A body is said to be in a rotatory motion or a circular motion if it moves about a fixed axis without changing the radius of its motion.
Examples : The blades of a fan, a spinning wheel.

Question 8.
What is meant by circular motion ? Give one example.
Answer:
The motion of a body along a circular path is called circular motion.
Example : A girl is whirling a stone tied at the end of a string in a circular path.

Question 9.
How does a rotatory motion differ from the circular motion?
Answer:
(i) In rotatory motion, the axis of rotation passes from a point
in the body itself whereas in circular motion, the axis of revolution passes through a point outside the body. Thus the motion of earth around the sun is the circular motion whereas the motion of earth about its own axis is the rotational motion.
(ii) In the circular and rotatory motions, the distance of a point of a the body from a fixed point always remains same, whereas it is not same in curvilinear motion.

Question 10.
Explain oscillatory motion by giving one example.
Answer:
Oscillatory motion— The to and fro motion of a simple pendulum is an oscillatory motion.
Example : 1. The motion of a swing, 2. Piston of an engine.

Question 11.
What is vibratory motion ? Give one example.
Answer:
In vibratory motion, a part of the body always remains fixed and the rest part moves to and fro about its mean position. During the vibratory motion, the shape and size of the body changes. Example : When we breath, our chest expands and contracts. This motion is vibratory motion.

Question 12.
Differentiate between periodic and non-periodic motions by giving an example of each.
Answer:
Periodic motion : A motion which gets repeated after regular intervals of time is called a periodic motion.
Examples : The earth moving around the sun takes 365 days to complete one revolution and this motion gets repeated after every 365 days.
Non-periodic motion : The motion which does not repeat itself after regular interval of time is called non-periodic motion.
Examples : A footballer running on a field, application of brakes in a moving vehicle, a ball rolling down the ground gradually slows down and finally stops, motion of tides in the sea, etc.

Question 13.
What is random motion. Give one example.
Answer:
Random motion— When an object in a motion has no specific path and which suddenly changes its motion is said to have a random motion.
Example : A flying kite.

Question 14.
Name the type/types of motion being performed by each of the following:
(a) Vehicle on a straight road
(b) Blades of an electric fan in motion
(c) Pendulum of a wall clock
(d) Smoke particles from chimney
(e) Hands of a clock
(f) Earth around the sun
(g) A spinning top.
Answer:
(a) Rectilinear motion
(b) Rotatory motion
(c) Oscillatory motion, periodic motion
(d) Non-periodic motion
(e) Uniform circular and periodic motion
(f) Rotatory motion, circular motion and periodic motion
(g) Rotatory motion

Question 15.
Give two examples to illustrate that a body can have two or more types of motion simultaneously.
Answer:
Sometime a body can have more than one type of motion. Such a motion is called the mixed motion.
Example :
(i) The wheels of a moving train have both the translatory as well as the rotatory motions as it moves from position A to position B while rotating.

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 6
(ii) The earth rotates about its axis (rotatory motion) and at the same time it revolves around the sun in a curved path (curvilinear or circular motion) in a fixed time interval (periodic motion).

Question 16.
State the types of motion of the following :
(a) The needle of a sewing machine
(b) The wheel of a bicycle
(c) The drill machine
(d) The carpenter’s saw
Answer:
(a) Periodic motion
(b) Rotatory motion
(c) Mixed = Translatory and Rotatory motion
(d) Mixed = Translatory and Oscillatory motion

Question 17.
Distinguish between uniform and non-uniform motions, giving an example of each.
Answer:

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 7

Question 18.
How do you determine the average speed of a body in non-uniform motion ?
Answer:
In a non-uniform motion, the average speed of a body is calculated by dividing the total distance travelled by the body, with the total time of its journey. Thus,
Average speed = Total distance travelled by the body / Total time of joumey

Question 19.
Define the term weight and state its S.I. unit.
Answer:
The weight of a body is the force with which earth attracts the body i.e. the weight of a body is the force of gravity on it. The weight of a body is not constant, but it changes from place to place. It is represented by the symbol W. The S.I. unit of weight is newton (N).

Question 20.
How are the units of weight, kgf and newton related ?
Answer:
1 kg F = 10 N

Question 21.
State three differences between mass and weight.
Answer:
Mass

It is the quantity of matter contained in a body.
Its S.J. unit is kilogram (kg)
It is constant for a body and it does not change by changing the place of the body.
It is measured by a beam balance.

Weight

It is the force with which the earth attracts the body.
Its S.I. unit is newton (N) and other unit is kilogram-force (kgf) where 1 kgf= 10N(nearly).
It is not constant for a body, but it changes from place to place.
It is measured by a spring balance.

Question 22.
Which quantity : mass or weight, does not change by change of place ?
Answer:
The mass of a body is constant and it does not change by changing the position of the body.

Question 23.
State which of the quantities, mass or weight is always directed vertically downwards.
Answer:
Mass is the quantity of matter contained in a body. Weight is the force with which the earth attracts the body. Weight is always directed vertically downwards.

 

C. Numericals

Question 1.
A car covers a distance of 160 km between two cities in 4 h. What is the average speed of the car ?
Answer:
Distance =160 km
Time taken = 4h
Speed = ?
Speed = Distance covered / Time taken
= 160km / 4h = 40 km h-1

Question 2.
A train travels a distance of 300 km with an average speed of 60 km h_1. How much time does it take to cover the distance?
Answer:
Speed = 60 km h-1
Distance covered = 300 km
Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 8

Question 3.
A boy travels with an average speed of 10 m s-1 for 20 min. How much distance does he travel ?
Answer:
Average speed of boy = 10 m s-1
Time taken = 20 min
Distance travelled = Speed × Time taken
Convert minutes into seconds
1 minute = 60 sec.
20 minutes = 20 × 60 = 1200 sec.
Distance travelled = 10 m s-1 × 1200 sec.
= 12000 m Or 12 km

Question 4.
A boy walks a distance 30 m in 1 minute and another 30 m in 1.5 minute. Describe the type of motion of the boy and find his average speed in m s-1.
Answer:
As the speed does not remain constant throughout the journey the motion is non-uniform
Total distance travelled in going and coming back
d = 30 m + 30 m = 60 m
Total time taken in going and coming back

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 9

Question 5.
A cyclist travels a distance of 1 km in the first hour, 0.5 km in the second hour and 0.3 km in the third hour. Find the average speed of the cyclist in
(i) km h-1, (ii) m s-1.
Answer:
(a) Distance travelled in first hour = 1 km
Distance travelled in second hour = 0.5 km
Distance travelled in third hour = 0.3 km
Total time taken = 3 hr
Total distance travelled = 1 + 0.5 + 0.3 = 1.8 km
(i) Average speed in km h-1

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 10
Average speed in m s-1
1 km = 1000 m
1.8 km = 1.8 × 1000 m
= 1800 m
1 hour = 3600 seconds
3 hour = 3600 × 3 = 10800 sec.

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 11

Question 6.
A car travels with speed 30 km h-1 for 30 minute and then with speed 40 km h-1 for one hour. Find :
(a) the total distance travelled by the car
(b) the total time of travel, and
(c) the average speed of car
Answer:
Speed of car for first 30 minutes = 30 km h-1
Speed of car for next 1 hour = 40 km h-1
(a) Total distance travelled by the car

Selina Concise Physics Class 7 ICSE Solutions Chapter 2 Motion 12

Question 7.
On earth the weight of a body of mass 1.0 kg is 10 N. What will be the weight of a boy of mass 37 kg in (a) kgf (b) N ?
Answer:
Weight of a body of mass 1.0 kg body = 10 N
(a) Weight of a boy of mass = 37 kg
(b) Weight of a boy of 37 kg in newton will be 1 kgf = 10N
∴ 37 kgf = 37 × 10 N
= 370 N

Question 8.
The weight of a body of mass 6.0 kg on moon is 10 N. If a boy of mass 30 kg goes from earth to the moon surface, what will be his (a) mass, (b) weight ?
Answer:
(a) Mass remains same it does not change
So mass of boy 30 kg on earth = 30 kg on moon surface
(b) Weight of boy on moon becomes 1 / 6
∴ 30 kg boy will weight 30 x 1/6 = 5kg
1 kg = 10 N ⇒ 5 × 10 N = 50 N
∴ Weight of boy on moon surface = 50 N

 

 

 

Selina Concise Chemistry Class 6 ICSE Solutions – Matter

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

Selina Class 6 Chemistry ICSE SolutionsPhysicsBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 6 Chemistry Chapter 3 Matter

POINTS TO REMEMBER

  1. Horse, mango tree, dog, animals, plants are living, while stone, pen, glass, water, book, table, air are non-living.
  2. All the above mentioned things living and non-living are matter.
  3. Energies like light, sound, heat are not matter, as these have no mass.
  4. Matter : “Anything that has mass and occupies space is called matter.” Matter (mass) remains same at all places.
  5. Molecules of matter are in motion.
  6. The things which are similar in one or more ways are grouped together and this practice is classification.
  7. There are inter-molecular gaps (spaces) and inter-molecular attraction (force of attraction) between molecules.
  8. Solids are rigid, have definite volume, retain their shape and are incompressible.
  9. Liquids can flow, have definite vol., have no definite shape. Have only one free surface.
  10. Gases Have no definite volume, no definite shape can flow are compressible.
  11. Inter-molecular force : Solids > Liquids > Gases.
  12. Inter-molecular volume : Solids < Liquids < Gases.

Activity 1

Question 1.
List five substances made using each of the following materials:
Answer:

  1. Wood : Chair
  2. Paper : Book
  3. Plastic : Bucket
  4. Metals : Copper wire
  5. Leather : Shoes
  6. Cloth : Shirt or bag

EXERCISE- I

Question 1.
Define matter.
Answer:
Anything that has mass and occupies space is called matter.

Question 2.
What are the two main types of matter? Give two examples for each type.
Answer:
The two main types of matter are :

  1. Living matter: The earth is home to all kinds of plants and animals. They can grow, move and reproduce on their own. Examples : Plant, lotus, animals, human etc.
  2. Non-living matter : Most of the matter in the universe is non-living. It means that it does not grow, move or reproduce on its own. It can be natural or man made.

(a) Natural matter: It occurs in nature and can be used to make more useful substances, e.g., wood, coal, silk, water, stone, cotton, jute, cereals, fruits, etc.
(b) Man-made matter : It is produce artificially from natural matter, e.g., plastics, soaps, detergents, medicines, glass, nylon, steel, ceramic, etc.

Question 3.
Differentiate between living and non-living matter.
Answer:
Living matter:

  1. The earth is home to all kinds of plants and animals. They can grow, move and reproduce on their own.
  2. It is natural only.

Non-living matter:

  1. Most of the matter in the universe is non-living. It means that it does not grow, move or reproduce on its own.
  2. It can be natural or man made.

Question 4.
Select natural and man made matter from the following
list: Wood, plastic, silk, medicines, detergents, coal, water, ceramic, cotton, glass, nylon, fruits.

Answer:
Natural matter: Wood, silk, coal, water, fruits.
Man made matter: Plastic, medicines, detergents, ceramic, cotton, glass, nylon.

EXERCISE-II

Question 1.
Name the smallest particle from which matter is made up.
Answer:
The smallest particle from which matter is made up is atom.

Question 2.
What are molecules ?
Answer:
Molecules are the smallest unit of matter. They exhibit all the properties of that kind of matter and is capable of independent existence.

Question 3.
Give one difference between atoms and molecules.
Answer:
Atoms may or may not have independent existance. While molecules have independent existence.

Question 4.
Define:
(a) Intermodular force of attraction.
(b) Intermodular space.

Answer:
(a) The molecules of matter are always in motion and attract each other with a force, and this force is called intermodular force of attraction due to which they are held together.
(b) The molecules can move only when there are gaps or space between them, this space is called intermodular space.

Question 5.
Name the three states of matter and define them.
Answer:
The three states of matter are :

  1. Solid State
  2. Liquids
  3. Gases :

Solid State : The molecules are very close to each other hence intermodular spaces are small and intermodular force is strong.
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 3 Matter 1
Hence solids have definite volume, rigid, retain definite shape and are incompressible.
Liquids : The molecules are less closely packed have more intermolecular spaces than solid, less stronger forces than solids.
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 3 Matter 2
Hence liquids have definite volume but no definite shape. They take the shape of container in which they are put.
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 3 Matter 3
Gases : The molecules in the gases are far apart with weakest force of attraction. Hence gases have neither definite volume nor definite shape but easily compressible.

Question 6.
What are fluids ? Give two examples
Answer:
Substances that can flow are called fluids. Both gases and liquids are fluids, e.g. gases (carbon dioxide, hydrogen), liquids (water, petrol and sulphuric acid).

Question 7.
Classify the following into solids, liquids and gases.
Oxygen, milk, common salt, wax, stone, L.P.G, carbon- dioxide, sugar, mercury, coal, blood, butter, copper, coconut oil, kerosene.
Answer:
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 3 Matter 4

Question 8.
Give reasons
(a) Liquids and gases flow but solids do not ?
(b) A gas Alls up the space available to it.
(c) The odour of scent spreads in a room.
(d) We can walk through air.
(e) Liquids have definite volume but no definite shape.
(f) When a teaspoon of sugar is added to half a glass of water and stirred, the water level in the glass remains unchanged.
(g) When an empty gas jar is inverted over a gas jar containing a coloured gas, the gas also spreads into the empty jar.
(h) A red ink drop added to small amount of water in a glass turns the water red in some time.

Answer:
(a) The molecules of liquids and gases are far apart i.e. have more gaps, intermolecular attraction force is very less as compared to solids, hence liquids and gases can flow but solids do not as gaps*in solid molecules is less and molecular force of attraction very strong.
(b) Intermolecular force of attraction is least and intermolecular spaces are very large, hence gases can fill up the space available to them.
(c) Scent fumes (molecules) being gases fill the spaces between air molecules and the molecules of air fill the spaces between scent molecules due to diffusion, fumes spread into a room.
OR
Due to inter-mixing of scent molecules and air molecules, scent fumes spread into the room.
(d) The molecules of air are far apart i.e. large gaps and we can walk through air easily.
(e) The molecules of liquid are loosely packed and intermolecular force of attraction is small but number of molecules in it remain the same. Hence liquids have definite volume but no definite shape.
(f) When a teaspoon of sugar is added to half a glass of water and stirred, the water level in the glass remains unchanged because the sugar particles are adjusted between the water molecules as inter-molecular gaps are more in liquids.
(g) This is because Gases can diffuse or flow in all directions.
(h) When we put a drop of red ink in a glass of water, its particles diffuse with particles of water slowly but continuously and the water turns red.

Question 9.
Define:
(a) cohesive force
(b) diffusion
(c) Brownian movement

Answer:
(a) Cohesive force : The force of attraction between particles of the same substance is called cohesive force.
(b) Diffusion: The phenomenon of intermixing of particles of one kind with another kind is called diffusion.
(c) Brownian movement: The zig-zag motion of particles suspended in a medium is called Brownian movement

Question 10.
Why is an egg kicked out of a bottle when air is blown inside the bottle?
Answer:
When we invert the bottle and blow air into the bottle throw the side opening. It creates high pressure inside the bottles and the egg is kicked out of the bottle.

EXERCISE-III

Question 1.
State the three effects of heat on matter.
Answer:
When a substance is heated, it can cause.

  1. Interconversion of states of matter.
  2. Thermal expansion of the substance.
  3. Chemical change.

Question 2.
(a) Define : interconversion of states of matter.
(b) What are the two conditions for the interconversion of states of matter ?

Answer:
(a) The process by which matter changes from one state to another and back to original state, without any change in its chemical composition.
(b) Two conditions are :

  1. Change in temperature
  2. By applying pressure

Question 3.
Define the following terms:
(a) Fusion
(b) Vaporisation
(c) Condensation
(d) Sublimation
(e) Diffusion
(f) Melting point
(g) Boiling point
(h) Liquefaction

Answer:
(a) Fusion : The heating process by which a solid changes into the liquid state is called fusion.
(b) Vaporisation : The heating process by which a liquid changes into its vapour state is called vaporisation.
(c) Condensation : The process by which a substance in gaseous state changes into its liquid state is called condensation.
(d) Sublimation: The change of solid on heating to vapours directly and vice-versa without passing through the liquid state is called sublimation.
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 3 Matter 5
(e) Diffusion : The phenomenon of intermixing or spreading of gaseous molecules is called diffusion.
(f) Melting point: The fixed temperature at which a solid changes into a liquid at a given pressure is called its melting point. The temperature remains constant as long as the conversion is going on.
(g) Boiling point: The fixed temperature at which a liquid starts changing into gaseous state is called its boiling point. The temperature remains constant till the whole of the liquid changes into gaseous state.
(h) Liquefaction : Change of vapours on cooling to liquid is called liquefaction.

Question 4.
Differentiate between:
(a) Solidification and condensation
(b) Melting and boiling
(c) Gas and vapour
(d) Miscible and immiscible liquids.

Answer:
(a) Solidification : The process of changing liquid into a solid state by cooling is known as solidification.
Example : water → ice.
Condensation : The process of changing a gas or vapour state to a liquid state by cooling is known as condensation. Example : steam → water.
(b) Melting : The fixed temperature at which a solid changes into a liquid at a given pressure is called its melting point.
e.g. ice → water.
Boiling : The fixed temperature at which a liquid starts changing into gaseous state is called its boiling point.
e.g. water → steam.
(c) Vapourisation : The process by which a substance changes from a liquid state to vapour state is called vaporisation or evaporation.
e.g., Water changes into gaseous state on heating.
Gas : The substance which remain in the gaseous state under normal conditions of temperature and pressure are called gases.
e.g, Oxygen, hydrogen, nitrogen.
(d) Miscible: Liquids which mix with each other are called miscible liquids. Example : Water and alcohol.
Immiscible liquids : Liquids which do not mix with each other are called immiscible liquids. Example Water and oil.

Question 5.
Give reasons :
(a) How is interconversion of states of matter different from chemical reaction ?
(b) Why a solid does not flow, but a liquid flows ?
Answer:
(a) During interconversion of state of matter composition
of substance remains the same matter changes from one state to another and back to the original state, while chemical reaction involves re-arrangement of the molecular structure and composition changes.
(b) In solids there is a strong force of attraction between the molecules and the space between them is very negligible. The molecules are therefore, not free to move. They merely vibrate about their mean positions. But in the case of liquids, the molecules are not very closely packed. They do not attract each other as strongly as the molecules of solids. Thus, the intermolecular spaces are larger and the molecules are able to move about more freely. This makes a liquid flow.

Question 6.
How does a liquid changes into its gaseous state? Explain ?
Answer:
As a liquid is heated, its particles starts gaining energy and move more vigorously which increases the gaps between the particles and decreasing the force of attraction. Ultimately a liquid changes into gaseous state.

Question 7.
Water cycle is an example of interconversion of states of water. Explain.
Answer:
Water from oceans, rivers, lakes from leaves of trees (transpiration) changes into vapours when temperature increases or evaporates and enters the atomsphere as clouds when temperature falls the vapours change into water and some of it in the form of snow fall on mountains and earth in the form of water and hales and this continues. Thus water cycle is example of interconvertion of states of water.

Question 8.
What happens to a metal ball when it is heated? What does this show?
Answer:
When metal ball is heated, it expands. This can be proved by following experiment:
Take a metallic ring and ball. Try to pass the metal ball through the ring. The ball is able to pass through the ring. Now heat the metal ball for 5-6 minutes. The hot ball is not be able to pass through the ring.
This shows that a solid expands on heating. Now cool the ball, it again passes through the ring. This shows that a solid contacts on cooling.
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 3 Matter 6

Question 9.
Why does a candle become smaller on burning with time?
Answer:
On heating, candle wax melts, then turns into vapour which reacts with air to produce two new substances, carbondioxide and water.
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 3 Matter 7
Therefore a candle on burning becomes smaller and smaller and the part of wax which has undergone chemical change cannot be recovered.

OBJECTIVE TYPE QUESTIONS

Question 1.
Fill in the blanks :

(a) Water is a matter because it has mass and occupies space.
(b) Any matter which has a definite volume but no definite shape is called a liquid.
(c) Liquids and gases can flow.
(d) The molecules are at a greater distance in gases compared to liquids.
(e) Water boils at 100 °C.
(f) The physical state of a substance, which has neither fixed volume nor fixed shape is a gas.

Question 2.
Write whether the following statements are true or false.

(a) Only water can exist in three different states.
(b) If the container in which a gas is collected has an opening, the gas will flow out and spread itself indefinitely.
(c) Solids have the large inter-molecular space.
(d) There is no difference between evaporation and boiling.
(e) All solids, on heating, first change to the liquid and then to the gaseous state always.
(f) The intermolecular force of attraction is the weakest in gases.
(g) A gas has no free surface.

Answer:
(a) True
(b) True
(c) False
Correct: Solids have the very small (negligible) inter-molecular space.
(d) False
Correct : There is a difference between evaporation and boiling.
(e) False
Correct : Few solids, on heating, first change to the liquid and then to the gaseous state always.
(f) True
(g) True

Question 3.
For each of the following statements, say whether it describes a solid, a liquid or a gas.

(a) Particles move about very quickly but do not leave the surface : Liquid
(b) Particles are quite close together : Solid
(c) Particles are far apart and move in all directions : Gas

Question 4.
Match the following :
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 3 Matter 8

Question 5.
Name the phenomenon which causes the following changes:
(a) Formation of water vapour from water.
(b) Disappearance of camphor when exposed to air.
(c) Conversion of ice into water.
(d) Conversion of water into steam.

Answer:
(a) Formation of water vapour from water is vaporisation.
(b) Disappearance of camphor is sublimation.
(c) Conversion of ice into water is melting.
(d) Conversion of water into steam is boiling.

Question 6.
Give two examples for each of the following :
(a) Substances which sublime.
(b) Substances which do not change their states.
(c) Substances which are rigid and not compressible.

Answer:
(a) Naphthalene, camphor, dry ice.
(b) Oxygen, hydrogen, nitrogen
(c) Glass, stone, pen.

MULTIPLE CHOICE QUESTIONS

1. Which one is a kind of matter :
(a) light
(b) petroleum
(c) sound
(d) heat

2. the state of matter which has no definite shape or volume is called
(a) solid
(b) liquid
(c) gas
(d) water

3. There are large intermolecular gaps in
(a) water
(b) iron ball
(c) common salt ..
(d) air

4. All kinds of matter
(a) occupy space and have a definite mass
(b) have mass and a definite shape
(c) can change their states
(d) have a definite volume

5. A kind of matter which can sublime is
(a) water
(b) plastic
(c) milk
(d) iodine

6. A substance which can change its state
(a) wood
(b) oxygen
(c) paper
(d) cloth

7. The process by which a solid changes into a liquid is called
(a) freezing
(b) melting
(c) condensation
(d) evaporation

PROJECT

Question 1.
Fill the following chart showing twelve solids, twelve liquids, four gases and eight materials.
Answer:
Solids : (1) Mobile. (2) Pen. (3) Pair of shoes. (4) A T.V. set (5) Chair. (6) Telephone. (7) Remote control. (8) Wood. (9) Ornaments. (10) Scissors. (11) Eraser. (12) Mirror.
Liquids : (1) Ink. (2) Water. (3) Lemon juice. (4) Cough syrup. (5) Mouth wash. (6) Petrol. (7) Kerosene oil. (8) Spirit. (9) Thinner. (10) Mercury. (11) Milk. (12) Copper sulphate solution.
Gases : (1) Hydrogen. (2) Oxygen. (3) Sulphur dioxide. (4) Chlorine gas.
Materials : (1) Paper. (2) Wood. (3) Iron nails. (4) Cement. (5) Tiles. (6) Plaster of paris. (6) Sand. (7) Iron rods. (8) Bricks.

Question 2.
Think and try to find a way to demonstrate water cycle in class.
Answer:
Do it yourself.

Question 3.
To identify materials of common use 
Procedure – Just move around in your house – in the drawing room, sitting room, bedroom, kitchen, bathroom etc.
Identify the things and All in the blanks in the table given below:

  • Study room
  •  Drawing room
  •  Kitchen
  •  bathroom
  • another place
S.No. PlaceName of the thingMaterial used for making the thing
  1. Study room
  2. Drawing room
  3. Kitchen
  4. bathroom
  5. Any other place

Answer:

S.No. PlaceName of the thingMaterial used for making the thing
1. Study roomTable, chair, books pens, pencils, table lamp, computer, fanWood, plastic, paper, glass, bakelite, connecting wires made of metal and plastics
2. Drawing roomSofa, table, chairs, fan, curtains, windows etc.Wood, cloth, coir, paint, plastics, aluminium, glass etc.
3. KitchenTaps, wash basin, cupboards, utencils, heating vessels strainer, containers aqua pure etc.Steel, aluminium, glass, china clay, iron, plastic, copper, stainless steel, brass etc.
4. BathroomTaps, tubs, mugs, tooth brush, tooth paste, soap, pail etc.Iron, brass, stainless steel, plastics etc.
5. Any other placeScooter, car, road, rooms, trucks, shops.Iron, rubber, coaltar, bricks, wood, plastics, clothes.