Heat Class 7th Question Answers

Heat is Chapter 4 taken from JKBOSE and NCERT textbook of Science for students of Class 7th. In the previous post, I provided you with Questions and Answers for Chapter 3 Fibre to Fabric. This post is about Heat Class 7th Question Answers. Before we move on to solutions you must have your basics clear. So, let me begin by giving you a brief overview of what you have studied in this chapter.

Heat Class 7th Question Answers

Overview of Chapter

• HOT AND COLD.
• MEASURING TEMPERATURE.
• LABORATORY THERMOMETER.
• TRANSFER OF HEAT.
• KINDS OF CLOTHES WE WEAR IN SUMMER AND WINTER.

HOT AND COLD: Heat is a form of energy which gives us a sense of warmth. We came across several objects in our daily life. Some of them are hot and some are cold. We usually decide whether a given object is hot or cold by touching it if it is not too hot or cold. 

MEASURING TEMPERATURE:  The degree of hotness or coldness of an object is termed temperature. Measuring the hotness or coolness of an object by the sense of touch is not a reliable way. So, it is measured by a device called a thermometer. The thermometer which is used to measure our body temperature is called a clinical thermometer. A clinical thermometer reads temperature from 35^o C to 42^oC. The normal human body temperature is 37C.

LABORATORY THERMOMETER: A thermometer which is used to measure the temperature of laboratory experiments and other objects is termed a laboratory thermometer. The range of a laboratory thermometer is generally from -10°C to 110°C. A laboratory thermometer cannot be used to measure the human body temperature because as soon as we take out the bulb of the laboratory thermometer from our mouth the level of mercury changes and it will give wrong values.

TRANSFER OF HEAT: The heat transferred from the hotter to the colder end of the object is called conduction and the objects which allow heat to pass through them are called conductors. The objects which do not allow heat to pass through them are known as insulators. The three ways through which heat can be transferred from a hot object to a cold object are: 1) By Conduction 2) By Convection 3) By Radiation. 

KINDS OF CLOTHES WE WEAR IN SUMMER AND WINTER: We used to wear light-coloured clothes in summer and dark-coloured clothes in winter. The reason for this is that light colours reflect most of the heat rays falling on them while dark colours absorb most of the heat rays falling on them. Also, we wear woollen clothes in winter which protect us from cold because wool is a poor conductor of heat. The air trapped in between the wool fibres does not allow the flow of heat from our body to the surroundings.

Exercises

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

Ans.  Similarities between the laboratory thermometer and the clinical thermometer.

1. Both thermometers are used to measure temperature.
2. Both temperatures are made of a long narrow uniform glass tube.
3. Mercury is used in the bulb of both thermometers.
4. Both of them have a Celsius scale marked on the glass tube.

Difference between laboratory a thermometer and a clinical thermometer.

1. A Laboratory thermometer is larger and broader in size as compared to a clinical thermometer.
2. The laboratory thermometer is used to measure the temperature of different objects while the clinical thermometer is used to measure the body temperature of human beings.
3. A clinical thermometer reads temperatures from 35⁰ C to 42⁰ C while a laboratory thermometer ranges from -10⁰ C to 110⁰ C
4. There is one kink in the clinical thermometer while there is no kink in the laboratory thermometer.

2. Give two examples each of conductors and insulators of heat.

Ans. Conductors of heat are the materials which allow heat to pass through them. For example Iron, steel, copper and aluminium etc.

Insulators of heat are materials which do not allow heat to pass through them. For example Plastic, paper, wood, water and air etc.

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 Celsius.

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

(e) A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end through the process of conduction.

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

4. Match the following:

Column I	Column II
(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

Ans.

Column I	Column II
(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

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

Ans. Wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing because a layer of air is trapped between different layers of clothes and the air is a poor conductor of heat. It prevents the flow of heat from our body to the surroundings and thus keeps us warm.

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

Ans. Heat is transferred in three manners in the given figure.

1. a) By Radiation: Heat is transferred from the flame to the bottom of the pan and from the vessel to the surroundings by the process of radiation.
2. b) By Conduction: Heat is transferred from the lower surface to the upper surface of the vessel by the process of conduction.
3. c) By Convection: Heat is transferred from pan to water by the process of convection.

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

Ans. White or light-coloured surfaces reflect most of the heat radiations falling on them. So, in places of hot climate, it is advised that the outer walls of houses be painted white because it does not absorb any heat radiations from the sun and keeps the houses cool inside.

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      

Ans. (d) between 30°C and 50°C because water at 30°C gains some heat while water at 50°C losses some heat.

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

(a) flow from the 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. 

Ans. (b) not flow from iron ball to water or from water to iron ball because both iron ball and water have the same temperature and heat can flow from higher temperature to lower temperature.

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.

Ans.  (d) does not become cold because wood is an insulator.

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 stainless steel.

(d) copper is easier to clean than stainless steel.

 Ans.  (c) copper is a better conductor of heat than stainless steel. So, stainless steel is usually provided with copper bottoms.

That’s all about Heat Class 7th Question Answers. Hope it has helped. Do share your views about this post in the comment section below.