CBSE Class 7 Science Heat Electric Current And Its Effects Worksheet

HEAT

Do you know, why?

1. The thick glass tumblers break when hot liquid is poured into them

Ans: If boiling hot water is poured in a thick glass tumbler, it cracks because glass is a bad conductor of heat. Thus, the inner surface of tumbler expands more than the outer surface. Due to this uneven expansion, the glass cracks.

2. Gaps are left between rail joints to allow for expansion

Ans: A small gap is kept at joints to allow for the expansion of tracks. If no gap is left for expansion or contraction, they will bend in summer. Thus, result in derailment of trains.

3. Slabs of ice are covered with sawdust or gunny bags

Ans: The saw dust or gunny bags contain large amount of trapped air which acts as an insulator. So, it doesn‟t allow the heat from outside to reach ice.

4. If we walk barefoot on a stone floor,it appears to be very cold but if walk on a carpet in the same room it feels warmer.

Ans: It is so because stone floor being a good conductor of heat, conducts away heat quickly from our feet. Our feet lose heat and make us feel cold. On the other hand, the carpet being a bad conductor of heat does not allow the heat of our feet to escape and hence feels warmer.

5. Solar cookers and solar water heaters are painted black from inside. Ans: This is because black surfaces are good absorber of heat.

6. Convection currents are produced inside the earth‟s crust.

Ans: Molten rocks close to the earth‟s core are hottest. It rises towards the crust. Molten rocks closer to the earth‟s crust are cooler. It is heavier and sinks. This exchange of material between core and crust create convection currents which move huge pieces of earth‟s crust known as tectonic plates. The tectonic plates move close together or farther, forming mountains and trenches.

MODULE – 1

I. Fill in the blanks:

(i) The liquid used in thermometer usually is____________ .

(ii) Normal body temperature of a human is _____ C &______F.

(iii) SI unit of heat is ________.

Q.1 Give one word for the following:

a. The mode of transfer of heat from one particle to another in solids.

b. Safety device in an electric circuit.

c. Filament of a bulb is made up of this metal.

d. Thermometer ranges from 35 C to 42 C.

e. Principle on which room heater works.

Q.2 Give reason for the following statements:

a. MCBs are used in place of fuses in homes and offices nowadays.

b. CFLs are being encouraged to be used in place of bulbs.

c. We prefer wearing dark coloured clothes in winters.

d. Ventilators are made close of the ceiling.

e. Electromagnets are temporary magnets.

Q.3 Shyam used a fuse wire with a specification of 5 A in a circuit connected to an air conditioner which draws a current of 10 A. What will happen when the air conditioner is switched on? What can be advised him to do?

Q.4 Tick the correct option:

(1) Which colour absorbs minimum radiation?
a. white
b. Black
c. yellow d.silver

(2) The device used to close or open an electric circuit is
a. Switch
b. resistance
c. ammeter
d. voltmeter

(3) Who discovered the magnetic effect of current?
a. Joule
b. Maxwell
c. Oersted
d. Newton

(4) Room heater works on the principle of
a. Conduction
b. convection
c. Radiation
d. insulation

(5) An electric bell makes use of
a. Bar magnet
b. needle shaped magnet
c. electromagnet
d. none of these

Q1. List two main effects of heat.

Q2. Define Temperature.

Q3.What do you understand by upper fixed point and lower fixed point?

Q4.Why is mercury and not water used in thermometers?

Q5. Name the scales used to measure temperature.

Q6. Give reasons for the following

i) Table mats are made from cane or plastics.

ii) Ventilators are situated close to the ceiling.

iii) Handles of bikes and scooters are covered with rubber.

iv) We cannot use laboratory thermometer to measure our body temperature.

v) We prefer to wear white clothes in summer

vi) Heating coils of a room heater have a shiny curved metal surface.

vii) Solar cookers are painted black from inside.

Q7.When you keep an ice cube on your palm, it melts slowly. From where does the flow of heat takes place?

Q8. Distinguish between:

i) Conduction and Convection

ii) Conductors and Insulators

Q9. How laboratory thermometer does differ from clinical thermometer?

Q10. Draw a neat and labeled diagram of clinical thermometer and explain the purpose of the kink in its stem.

I. Give one word for the following.

1) The degree of hotness or coldness of a body.

2) Metal used in thermometers.

3) Instrument used to measure temperature of a body.

4) Materials that allow heat to pass through them easily.

5) Materials that do not allow heat to pass through them.

I. Fill in the blanks.

1) Air is a ________ conductor of heat.

2) Solids ________ on cooling.

3) Heat is a form of energy that travels from a _______ object to a _______ object.

4) A spoon kept in a cup of hot tea gets heated by _________

5) The normal body temperature is _______ oC or _____o F.

6) ________ is the best conductor of heat.

7) Ice melts at ______ oC or ______ oF.

8) Water boils at _______oC or ______oF.

9) Black bodies ________ and emit ________ heat the best.

10) The another name of clinical thermometer is __________ thermometer.

II. State true or false.

1) Heat cannot travel in vacuum.

2) Gases expand the most while solids expand the least on heating.

3) Room heaters warm the rooms by conduction.

4) Blankets keep us warm at night in winters.

5) The wooden handle of a pressure cooker prevents conduction of heat to the hand.

III. Match the following.

              A                              B

1) Conduction                 a) day

2) Radiation                    b) solids

3) Heat                           c) night

4) Sea Breeze                d) energy

5) Land Breeze              e) vacuum

IV. Define.

i) Energy

ii) Temperature

iii) Conduction

iv) Convection

v) Radiation

V. Give reasons

i) Evaporation of sweat causes cooling.

ii) Ventilators are provided near the ceiling of a room.

iii) Clinical thermometers have a kink in the capillary tube

VI. Draw the diagram of the following:

i) Sea Breeze

ii) Land Breeze

1.What is the range of laboratory thermometer?

2.The capillary tube of a clinical thermometer has kink-
(A) To increase the expansion of mercury.
(B) So that the level of mercury does not fall as soon as the thermometer is taken out of the mouth.
(C) To use less mercury.
(D) To help us see it better.

3.Radiation
(A) Does not require a material medium.
(B) Is the process of the transfer of heat in liquids.
(C) Is the process of the transfer of heat in which heat travels in one direction.
(D) Occurs in solids.

4.Human body temperature is normally-
(A) 32°F.
(B) 0°F.
(C) 100.4°F.
(D) 98.6°F

5.The range of a clinical thermometer is-
(A) 0-100°C.
(B) 32-212°F.
(C) 0-273°C.
(D) 35-42°C.

6.The measure of degree of hotness or coldness of body is called-
(A) Heat energy.
(B) Celsius.
(C) Kelvin.
(D) Temperature.

7.The capacity to do work is called-
(A) Force.
(B) Movement.
(C) Energy.
(D) Momentum.

8.How can we measure the temperature of our body?

9.What is the temperature of a normal human body?

10.What is the use of the kink in clinical thermometer?

11.What is the range of the clinical thermometer?

12.Name a thermometer which does not use mercury as one of it's component?

13.Name the process by which heat is transferred from hotter object to the colder object.

14.What is the process by which heat of sun is able to reach us?

15.What is temperature?

16.Can we measure the temperature of 45°C from a clinical thermometer?
(A) No.
(B) Yes.
(C) Sometimes.
(D) From some clinical thermometers.

17.Heat of the Sun reaches to us by-
(A) Reflection.
(B) Condensation.
(C) Radiation.
(D) Sunlight.

18.Define conduction.

19.How does heat flow?

20.What will happen to a clinical thermometer if we keep it in the Sun or near a flame?
(A) It will measure the temperature.
(B) It will break.
(C) It will melt.
(D) Nothing will happen.

21.What is temperature ?

22.Name the mode of heat transfer in which heat energy flows from one body to another only if they are in contact with each other ?

23.Name the mode of heat transfer in which heat is transferred even in the absence of a medium ?

24.Temperature is the degree of or …………………..of a body.

25.The hotness of a body is determined by its…………………

26.A clinical thermometer can measure a temperature between ... °C and……………°C.

27.No medium is required for transfer of heat by the process of

28.A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of ……………………..

29. is the process of transmission of heat in which heat travels directly from one place to another without the agency of any intervening medium.

30.The cold air blowing from the sea towards the land during the day is called ………………

31.The cold air blowing from the land towards the sea during night is called ………………..

32.Clothes of light colours are better………………….of heat than clothes of dark colour.

33.What is the value of the normal body temperature ?

<2M>

34.In places of hot climate, it is advised that the outer walls of houses should be painted white. Explain.

35.Explain why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of cloth?

36.How does the heat travel in air? In which direction does the smoke go?

37.What are the 2 conditions for conduction to take place?

38.What is temperature? Name the device used to measure it.

39.Name the two common scales in which temperatures are usually measured ?

40.Why a clinical thermometer should not be washed in hot water ?

41.Why in places of hot climate it is advised that the outer walls of houses be painted white.

42.Why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.

43.Why do we wear woollen clothes in winter ?

44.What kind of clothes will keep us comfortable in summer ? Why ?

45.Describe the construction of a clinical thermometer

<3M>

46.What are conductors and insulators of heat? Give examples.

47.Write any three similarities between laboratory thermometer and the clinical thermometer.

48.What do you understand by clinical thermometer and laboratory thermometer?

49.differentiate between heat and temperature

<5M>

50.Suggest an activity to explain the term convection. >

51.Explain the process of conduction with the help of activity and neat labeled diagram

52.How will you read a thermometer?

53.What are the precautions to be take while reading a clinical thermometer?

54.Write short notes on :-
(a) Sea breeze .
(b) Land breeze.

55.What precautions will you observe while using a clinical thermometer ?

56.write the differences between a clinical thermometer and a laboratory thermometer ?

57.write the differences between a clinical thermometer and a laboratory thermometer ?

Q.1 Multiple choice Question

1. The clinical thermometer’s bulb consists of

a. lead

b. mercury

c. Zinc

d. None of these

2. Which of the following materials are good conductors of heat?

a. Iron

b. Copper

c. Silver

d. None of these

3. Water is a _____________ conductor of heat.

a. good

b. bad

c. both

d. None of these.

4. The process of transfer of heat in which the heated molecules of a liquid themselves carry heat from the hot to the cold region?

a. Conduction

b. Convection

c. Radiation

d. None of these

5. Sea breeze and land breezes are actually

a. Currents

b. Water currents

c. waves

d. Convection currents

Q.2 Answer the following questions

a. Why are cloudy nights warmer than clear nights?

b .How do the feathers of a bird protect it from cold ?

Q1. Fill ups:

a) ____________ is the degree of relative hotness or coldness.

b) Cooking vessels should be made up of __________ conductors.

c) Heat is a form of ___________.

d) Mercury level falls easily in a _____________thermometer.

e) S.I unit of heat is __________________.

f) Range of clinical thermometer is from __________̊C to ________̊C.

g) A kink is not provided in a ___________ thermometer.

Q2. Choose the correct option:

1) Conduction takes place in:
a) Solids only
b) Liquids only
c) Gases only
d) in solids, liquids & Gases

2) In which method of transfer of heat do the molecules travel from hot to cold portion?
a) Conduction
b) Convection
c) Radiation
d) All of the above

3) A thermos flask prevent loss or gain of heat by
a) Conduction
b) Convection
c) Radiation
d) All of the above

4) Convection occur only in
a) Solids
b) Liquids
c) Gases
d) Liquids & Gases

5) Ventilation in the room is due to:
a) Conduction
b) Convection
c) Radiation
d) All of the above

6) The method of heat transfer in a steel rod is by:
a) Conduction
b) Convection
c) Radiation
d) All of the above

Q3. Why is underside of cooking vessels painted black?

Q4. Why do we feel cold when our body sweats?

Q5. Why only mercury is used in thermometer?

Q6. Explain three modes of transmission of heat i.e. conduction, convection & radiation, with the help of their applications.

Q7. Name the following:

a) Fastest mode of transfer of heat._____________

b) Mode of transfer of heat where the medium does not get heated.___________

c) Mode of transfer of heat where no medium is required.______________

d) The metal used in the bulb of thermometer.___________________