# NCERT Class 7 Science Chapter 3 Heat: Notes and Solutions (Free PDF)

NCERT Class 7 Science Chapter 3 on Heat defines temperature and teaches us about different types of thermometers- clinical thermometers and laboratory thermometers. Further, we explore different modes of heat transfer- conduction, convection, and radiation. Also, we get to know about the phenomena of sea breeze and land breeze, which helps us get clarity on heat transfer via convection. To help you understand all these Class 7 Science topics, we have created these notes. In addition, the notes also provide you with NCERT solutions to writing questions following the chapter.

## Temperature and Ways to Measure Temperature

Let us start learning NCERT Class 7 Science Chapter 3 by exploring definitions and concepts related to temperature and the measurement of temperature.

### Temperature

The measure of hotness or coldness of an object is termed as “Temperature”.

### Thermometer

The thermometer is a device used to measure the temperature of an object. There are two kinds of thermometers- Clinical thermometers and Laboratory thermometers.

### Clinical Thermometer

A clinical thermometer is used to measure the human body temperature only. It is used at homes and by doctors and nurses in hospitals, clinics, and nursing homes.

Here are some features of a Clinical Thermometer:

• Structure: A clinical thermometer comprises an elongated, slender, even glass tube with a reservoir at one end that holds mercury. The mercury is visible within the reservoir in a small, shining column.
• Scale/Range: A clinical thermometer with a Celcius scale reads temperature from 35°C to 42°C. Whereas, one with a Fahrenheit scale reads temperature from 94°F to 108°F.
1. Initially, observe the temperature variation displayed between the two larger indicators.
2. Additionally, take note of the number of divisions situated between these indicators.
3. If the larger indicators represent one degree, and there are five divisions between them, then each small division corresponds to 0.2 degrees Celsius.
• Precautions to use a Clinical thermometer:
1. Clean the thermometer, especially with an antiseptic solution, before and after using the thermometer.
2. Make certain that the mercury level is below 35°C before employing the thermometer.
3. When reading the thermometer, ensure that the mercury level aligns with your line of vision.
4. Exercise caution in handling the thermometer to prevent it from shattering if it comes into contact with a solid object.
5. Avoid gripping the thermometer by the bulb when taking readings.
• Normal Temperature of a Human Body: 37°C

### Laboratory Thermometer

A laboratory thermometer is used to measure the temperature of objects other than human beings.

Here are some features of a Clinical Thermometer:

• Sacle/Range: Typically, a laboratory thermometer has a temperature range that spans from -10°C to 110°C.
• Precautions to use a Laboratory Thermometer:
1. Maintain the thermometer in an upright position and avoid tilting it.
2. Ensure that the bulb is fully surrounded by the material for which you are measuring the temperature. The bulb should not come into direct contact with the surface of the container.

## Heat Transfer

Heat transfer is an important topic in the NCERT Class 7 Science Chapter 3. In this section, we learn about ways of heat transfer and associated phenomena like Sea Breeze and Land Breeze.

### Conduction

The phenomenon in which heat is transferred from the warmer end to the cooler end of an object is referred to as “Conduction”. In solids, heat is usually transferred via conduction.

### Convection

Convection is the process of heat transfer in fluids (like liquids and gases) where warmer portions rise and cooler parts sink, creating a circulation or flow of the fluid. It is commonly seen in activities like boiling water or in the Earth’s atmosphere and oceans, land breeze, and sea breeze.

Radiation is the transfer of heat in the form of electromagnetic waves, such as light or heat from the sun. Unlike conduction and convection, radiation does not require a medium (like air or water) to transfer heat; it can travel through a vacuum.

Also Read: Moon Surface Temperature: ISRO Findings

## NCERT Solutions Class 7 Science Chapter 3: Heat

In this part of our notes, our subject experts have answered all written questions in the “Exercises” of NCERT Class 7 Science Chapter 3.

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

Ans:
Here are the similarities:

• Both are typically constructed using glass, and they consist of a long, narrow glass tube.
• They both have a bulb at one end, which is used to measure the temperature of the substance or the body.
• Traditionally, both types of thermometers use mercury in the bulb. However, due to the environmental hazards associated with mercury, modern versions may use other materials.
• Both the clinical and laboratory thermometers commonly use the Celsius scale for temperature measurement, which is widely recognized and utilized globally.

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

Ans:

• Examples of Conductors: Iron and Aluminium
• Examples of Insulators: Wood and Plastic

Ques 3. Fill up 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 the 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. Temperature

b. Clinical

c. Celsius

e. Conduction

f. Dark

Ques 4. Match the items from Column I with that in Column II

Ans:

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

Ans: Wearing multiple layers of clothing in winter is more effective in keeping us warm compared to wearing a single, thick garment because it creates pockets of trapped air between the layers. Since air is a poor conductor of heat, it acts as an insulator and prevents the escape of body heat. Thus, it provides better insulation against the cold.

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

Ans: In regions with hot climates, it is recommended to paint the exterior walls of houses white because white colour has a highly reflective property. This means it bounces back a significant portion of the heat from the sun. White surfaces are also less efficient at absorbing heat, and this strategy effectively contributes to maintaining a cooler indoor environment in the house.

Ques 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

Ques 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: b.  not flow from iron ball to water or from water to iron ball.

Ques 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.

Ques 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 stainless steel.

Ans: c. copper is a better conductor of heat than stainless steel.