Class 7 Science Chapter 4 Notes

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Class 7 Science Chapter 4 Notes

Chapter Name: - Heat

Class 7 Science Chapter 4 Notes

Section - A (Keywords)

Explain the following Keywords

The scale used for measuring the temperature with its reference points at 0º C for the freezing point of water and at 100º C for the boiling point of water.

Celsius scale was developed by a Swedish astronomer, Anders Celsius.

Read More: – Celsius Scale

Read More: – Heat and Temperature: All Must Know Points

The mode of transfer of heat in the solids substances.

The substances which allow heat and electricity to pass through them.

Examples: –
Copper, aluminium, iron

The mode of transfer of heat in the liquid and gases.

The breeze that originates from the sea and flows towards land.

Read more: – Land Breeze Vs Sea Breeze

Temperature is used to measure the heat possessed by an object. The SI unit of temperature is Kelvin.

Read More: – Kelvin Scale

The device used to measure the temperature is called thermometer.

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Class 7 Science Chapter 4 Notes

Section - B (Text Questions - Answer)

Question 1

State similarities and differences between the laboratory thermometer and the clinical thermometer.

Similarities between the laboratory and the clinical thermometer

1. Both are used to measure the temperature in Celsius or Fahrenheit.

2. Both the thermometers have mercury as medium of transfer of heat. So, we can say that their working principle is the same.

3. The materials for the design of both the thermometer are almost the same such as a bulb, and a glass tube. 

Differences between the laboratory and the clinical thermometer

1. Range: The range of a clinical thermometer is 35ºC to 42ºC, whereas the range of a laboratory thermometer is -10ºC to 110ºC.

2. Purpose: The clinical thermometer is designed to measure the human body temperature only whereas the laboratory thermometer is used to measure the temperature of many different objects.

3. Use of kink: A kink is used in the clinical thermometer to prevent the mercury level from falling on its own.

Question 2

Give two examples each of conductors and insulators of heat.

The substances which allow heat and electricity to pass through them are called conductors.

Examples of Conductors of heat: – copper and aluminum.

The substances which do not allow heat and electricity to pass through them are called insulators.

Examples of the insulators of heat: – wood and plastics.

 

 

Question 3

Fill in the blanks :

(a) The hotness of an object is determined by its temperature.

(b) Temperature of boiling water cannot be measured by a clinical thermometer.

(c) Temperature is measured in degree Celcius.

(d) No medium is required for transfer of heat by the process of radiation.

(e) A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of conduction.

(f) Clothes of dark colours absorb more heat better than clothes of light colours.

Question 4

Match the following :

(i) Land breeze blows during(a) summer
(ii) Sea breeze blows during (b) winter
(iii) Dark coloured clothes are preferred during(c) day
(iv) Light coloured clothes are preferred during (d) night
(i) Land breeze blows during(d) night
(ii) Sea breeze blows during (c) day
(iii) Dark coloured clothes are preferred during(b) winter
(iv) Light coloured clothes are preferred during (a) summer

Question 5

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

The air gets trapped between the more layers of clothing. During winter, the upper cloth gets cold. The air, that is present between these layers, blocks the coldness of the atmosphere to pass to the second layer of clothing. As, the air is a poor conductor of heat.

Also, the air that is trapped between the many layers of clothing, prevents our body heat to escape into the cold atmosphere.

Question 6

Look at Fig. 4.13. Mark where the heat is being transferred by conduction, by convection and by radiation.

Look at Fig. 4.13. Mark where the heat is being transferred by conduction, by convection and by radiation.

Look at Fig. 4.13. Mark where the heat is being transferred by conduction, by convection and by radiation. - Copy

Conduction: from the metallic stand to the metallic pan.

Reason: Conduction is the mode of heat transfer in the solids.

Convection: From the water at the bottom layer to the water at the upper layer in the pan.

Reason: Convection is the mode of heat transfer in the fluids (liquids and gases).

Radiation: In the atmosphere all around the gas burner.

Reason: Radiation is the transfer of heat around a hot body. No medium is required for the transfer of heat for radiation.

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Class 7 Science Chapter 4 Notes

Question 7

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

In places of the hot climate, it is advised that the outer walls of houses be painted white. Because the white colour reflects most of the heat that falls on them. Therefore, the walls of the house absorb very little heat in the hot climate.

Question 8

One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture will be

(a) 80°C (b) more than 50°C but less than 80°C
(c) 20°C (d) between 30°C and 50°C

Option (d) between 30°C and 50°C.

Reason: The heat flows from the body at a higher temperature to the body at a lower temperature.

In this case, the heat from the water at 50°C will transfer to the water at 30°C. The temperature of the water at 30°C will rise and the temperature of the water at 50°C will come down to a common temperature between 30°C and 50°C.

Question 9

An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will

(a) flow from iron ball to water.
(b) not flow from iron ball to water or from water to iron ball.
(c) flow from water to iron ball.
(d) increase the temperature of both.

Option (b) not flow from iron ball to water or from water to iron ball.

Reason: As the temperature of both the objects is the same, So, no transfer of heat will take place.

Question 10

A wooden spoon is dipped in a cup of ice cream. Its other end

(a) becomes cold by the process of conduction.
(b) becomes cold by the process of convection.
(c) becomes cold by the process of radiation.
(d) does not become cold.

(d) does not become cold.

Reason: The wood is an insulator of heat. So, the heat will not get transferred from one of its end to the other.

Question 11

Stainless steel pans are usually provided with copper bottoms. The reason for this could be that

(a) copper bottom makes the pan more durable.
(b) such pans appear colourful.
(c) copper is a better conductor of heat than the stainless steel.
(d) copper is easier to clean than the stainless steel.

Option: (c) copper is a better conductor of heat than stainless steel.

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Class 7 Science Chapter 4 Notes

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