03. Heat Class 7 Science NCERT Notes for Chapter 3 CBSE

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Welcome to Heat Class 7 Science NCERT Notes for Chapter 3 CBSE.

Exam Notes: Heat class 7 chapter 3 (earlier it was chapter 4)

Introduction

In this chapter, we will explore the concept of heat, its measurement, and how it is transferred from one object to another. Understanding heat is essential for various everyday applications, from cooking to climate control.

3.1 Hot and Cold

In our daily lives, we encounter objects that are either hot or cold. To determine the relative hotness or coldness of objects, we often use our sense of touch. However, this method is not always reliable, and that’s where temperature measurement comes in.

Measurement with Thermometers

Temperature is a measure of an object’s hotness.
Thermometers are devices used to measure temperature.
Clinical thermometers are used to measure human body temperature and have a range of 35°C to 42°C.
Laboratory thermometers have a wider range, typically from -10°C to 110°C.

3.2 Measuring Temperature

Have you ever wondered how a thermometer measures temperature? Let’s explore the details.

Reading a Thermometer

To measure temperature, note the temperature difference between two larger marks on the thermometer‘s scale.
Count the number of divisions between those marks.
Calculate the value of each small division (e.g., 1 division = 0.2°C for a 5-division gap).

Precautions with Clinical Thermometers

Wash the thermometer before and after use, preferably with an antiseptic solution.
Ensure that the mercury level is below 35°C before use.
Handle the thermometer with care to avoid breakage.

3.3 Transfer of Heat

Heat can be transferred in three main ways: conduction, convection, and radiation.

Conduction

Conduction is the transfer of heat through solids.
Materials that allow heat to pass easily are called conductors (e.g., metals).
Materials that resist the flow of heat are called insulators (e.g., wood and plastic).

Convection

Convection is the transfer of heat through liquids and gases.
It involves the movement of heated particles, creating currents.
Hot air rises, and cold air sinks, leading to the circulation of heat.

Radiation

Radiation is the transfer of heat through electromagnetic waves.
It can occur without a medium (unlike conduction and convection).
All objects emit and absorb radiation, with dark-colored objects absorbing more heat than light-colored ones.

3.4 Kinds of Clothes We Wear in Summer and Winter

We choose our clothing based on the weather, and understanding how different materials behave with heat can help us make informed clothing choices.

Clothing in Summer

Light-colored clothes reflect heat, keeping us cooler.
They are comfortable because they absorb less heat.

Clothing in Winter

Dark-colored clothes absorb heat, making us feel warmer.
Woolen clothes are preferred in winter because wool is a poor conductor of heat and traps air, providing insulation.

Keywords and Their Definitions

Important Definitions for – heat class 7

Heat: Heat is the form of energy that flows from a hotter object to a colder one.
Thermometer: A thermometer is a device used to measure temperature.
Clinical Thermometer: A clinical thermometer is a specialized thermometer used to measure human body temperature.
Laboratory Thermometer: A laboratory thermometer is designed for general laboratory use and has a broader temperature range.

Conclusion

Understanding heat and temperature is crucial for daily life. Thermometers help us measure temperature accurately, and knowing how heat is transferred allows us to make informed decisions about clothing and energy use.

Frequently Asked Questions (FAQs)

Important Questions for – heat class 7 chapter 3.

Q1: What is heat?

A: Heat is a form of energy that flows from a hotter object to a colder one.

Q2: How do thermometers work?

A: Thermometers work by measuring the temperature difference between two points on their scale and counting the divisions in between.

Q3: Why should clinical thermometers be washed before and after use?

A: Clinical thermometers should be washed to maintain hygiene and prevent the spread of germs.

Q4: What is the difference between conduction and convection?

A: Conduction is the transfer of heat through solids, while convection occurs in liquids and gases through the movement of heated particles.

Q5: Why do dark-colored clothes feel warmer in winter?

A: Dark-colored clothes absorb more heat, making the wearer feel warmer.

Q6: What makes woolen clothes suitable for winter?

A: Woolen clothes are good insulators and trap air, providing warmth in cold weather.

Q7: Can heat be transferred through a vacuum?

A: Yes, heat can be transferred through radiation, even in a vacuum where there is no medium.

Q8: What materials are good conductors of heat?

A: Metals are excellent conductors of heat.

Q9: Why is it important to handle clinical thermometers with care?

A: Handling clinical thermometers with care prevents breakage and exposure to harmful substances like mercury.

Q10: How does the color of clothing affect heat absorption?

A: Light-colored clothing reflects heat, while dark-colored clothing absorbs heat.

This was the end of Heat Class 7 Science NCERT Notes for Chapter 3 CBSE.

For more information, refer to NCERT SOLUTIONS, NCERT NOTES, and NCERT BOOKS .