# NCERT Solutions for Class 7 Science Chapter 4 Heat

Class 7 plays a crucial role in introducing students to core concepts of Science that are further used in higher grades. This means that students need to pay special attention to this subject at this stage to build a strong foundation. To help Class 7 students with their Science preparation, Extramarks offers NCERT Solutions for Class 7 Science Chapter 4 Heat. These are detailed solutions to the questions given in Chapter 4 of their Science textbook. Since solving questions is a crucial part of their preparation, students will find these resources to be very useful with their preparations, last-minute revisions, and for help with their assignments.

## NCERT Solutions for Class 7 Science Chapter 4

### NCERT Solutions for Class 7 Science Heat

Chapter 4 – Heat

Heat is an essential element required for the continuation of life, especially for plants’ and animals’ lives. Chapter 4 of the Class 7 NCERT Science textbook introduces students to some of the crucial aspects of heat and gives an insight into topics like temperature, measuring temperature, transfer of heat, summer and winter clothes, and many more.

4.1 Hot and Cold

In our day-to-day lives, we come across several different items. Some objects feel hot, and some feel cold upon touching. For example, when an iron rod is exposed to heat or the sun for a longer time, it becomes hot, and when normal water is stored in the refrigerator, it becomes cold. We might not notice, but we keep switching between hot and cold throughout the day. The degree of hotness or coldness varies according to the objects and the situation. Now the question is, if we are given two objects, how can we tell which object is hotter?Although it can be figured out by touching the object, we still need something more concrete to measure heat.

4.2 Measuring Temperature

A reliable measure of the hotness of an object is temperature. A thermometer is an instrument or a device used to measure the temperature. We generally use a clinical thermometer to measure our body’s temperature in our house, but there are many variations of a thermometer. A clinical thermometer is made up of a glass pipe and is cylindrical. It has a bulb containing mercury at the bottom, where you can see a shining mercury thread. A clinical thermometer reads the temperature from 35-42 degree celsius

Remember to notice the temperature difference by two bigger marks when reading a thermometer. Always handle a thermometer very carefully because the mercury might leak out if it breaks.

4.3 Laboratory Thermometer

To take readings from other objects, a laboratory thermometer is used. Your science teacher can show you a laboratory thermometer present in the chemistry lab. The measuring scale of a laboratory thermometer is different from that of a clinical thermometer. It generally ranges from -10°C to 110°C. It is very important to note each reading very precisely to get accurate information.

Interesting Facts

The thermometers that we use today are a modified structure of the traditional thermoscopes invented by the famous scientist Galileo Galilei. Today the Fahrenheit and Celsius scales are used for measuring various types of temperatures in most cases, but earlier, there were as many as 35 scales by the 1700s. But finally, conclusions were made by Daniel Fahrenheit and Anders Celsius. Daniel Fahrenheit set the boiling point of water at 212 degrees and the freezing point was set at 32 degrees. The centigrade scale was developed by Anders Celsius, who then assigned 0 degrees to the boiling point of water and 100 degrees to the melting point of ice. The Fahrenheit and the Celsius scales are equal when they both reach a point of -40 degrees. The Kelvin and Rankine scales are used for other purposes in the laboratory.

4.4 Transfer of Heat

A frying pan becomes hot when placed on a flame. Have you ever thought about why? This happens because the heat passes through the source to the frying pan and cooks the food. This phenomenon is known as the transfer of heat. The frying pan eventually cools down when moved away from the flame. Why does this happen? The heat escapes through the floor or anything touching the pan. This proves that heat flows from hotter to cooler objects.

4.5 Kinds of Clothes We wear in Summer and Winter

We wear woollen clothes in winter and light cotton clothes in summer. Wool is a bad conductor of heat since its fibres trap the air inside it, thus keeping away the cold air from entering the body. The movement of heat gets obstructed by this trapped air. This is also why using two to three blankets in winter saves us from the cold. The air trapped between the blankets captures the heat and keeps us warm.

We wear light-coloured clothes in summer because light colour absorbs less heat and reflects more. This helps in preventing heat from entering the body, keeping it cold.

#### Key Features of NCERT Solutions for Class 7 Science Chapter 4

Extramarks is a comprehensive study platform that provides various valuable resources for students, which includes NCERT Solutions. The key features of NCERT Solutions for Class 7 Science Chapter are listed below.

• The solutions have been developed by subject matter experts who have years of experience in their respective fields.
• Subject experts take special care in providing accurate solutions in a step by step manner so that students can understand them properly.
• The solutions provided include detailed explanations along with examples and illustrations wherever required. Students can use these solutions for their exam preparations, last-minute revisions, and to get a sense of how they should frame solutions in their exams.

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

Ans-

Similarities between clinical and laboratory thermometers are as follows:

1. Both of them are used for measuring temperature.
2. Both of them use mercury as an indicator for rise and fall in temperature.

Differences between clinical and laboratory thermometers are as follows:

1. Clinical thermometer is used to measure body temperature whereas; laboratory thermometer is used to measure temperature of substances.
2. The range of clinical thermometer is from 35°C to 42°C while that of laboratory thermometer is from minus 10°C to 110°C.

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

The examples of conductors of heat are as follows:

1. Aluminium
2. Copper

Ans-

The examples of insulators of heat are as follows:

1. Wood
2. Rubber

Q.3 Fill in the blanks :
(a) The hotness of an object is determined by its __________.
(b) Temperature of boiling water cannot be measured by a _____________ thermometer.
(c) Temperature is measured in degree ______________.
(d) No medium is required for transfer of heat by the process of __________.
(e) A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of ______________.
(f ) Clothes of ______________ colours absorb more heat better than clothes of light colours.

Ans-

(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 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.

Q.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

Ans-

The correctly matched contents of the two given columns are as follows:

 (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

Q.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 in between the multiple layers of clothing, air is trapped that prevents the loss of heat from the body to the surroundings. Air is a poor conductor of heat and prevents the transfer of heat from one region to the other. This trapped air in between the layers of clothing keeps us warmer than the single thick clothing.

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

Ans-

Various modes of transfer of the heat in the given diagram can be shown as follows:

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

Ans-

The outer walls are advised to be painted white in hot climate conditions because white colour reflects maximum amount of heat back into the surroundings, that falls on it. Therefore, white coloured walls absorb least amount of heat and keep the house cool.

Q.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- Correct option is (d).

Explanation:
As heat will flow from one litre of water at 50°C to one litre of water at 30°C, so the temperature of the mixture will be between 30°C and 50°C.

Q.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

Ans- Correct option is (b).

Explanation:
As both the water and the iron ball have the same temperature, so the heat will not flow from iron ball to water or from water to iron ball.

Q.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- Correct option is (d).

Explanation: Wood is a bad conductor of heat.

Q.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

Ans- Correct option is (c).

Explanation:
Copper is a good conductor of heat, so it allows the heat to distribute evenly throughout the utensil, and heats the stainless steel pans faster.