Chapter 4 – Heat

These NCERT Class 7 Science Chapter 4 notes explain the concept of heat and its importance in our daily life. The chapter helps students understand the difference between heat and temperature and why touch is not a reliable method to measure hotness or coldness.

Heat also explains how heat flows from one object to another, different modes of heat transfer, and practical examples like sea breeze, land breeze, and the use of woollen clothes. This chapter builds a strong foundation for understanding thermal concepts.

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1. Introduction: why heat is important

•  Heat is a form of energy that affects temperature, state of matter, and daily life activities.
•  We feel hot or cold using touch, but touch is not reliable for judging heat.
•  The same object may feel hot to one person and cold to another.

2. Hot and cold objects

•  An object is called hot if it has more heat, and cold if it has less heat.
•  Sense of touch cannot measure temperature accurately, so it can be misleading.

3. Measuring temperature

•  Temperature tells how hot or cold an object is.
•  Temperature is measured using a thermometer, not by touch.

4. Thermometer

•  A thermometer measures temperature using the expansion of liquids.
•  A clinical thermometer measures body temperature, has a range of 35°C to 42°C, and normal body temperature is 37°C.
•  A kink in the clinical thermometer prevents mercury from flowing back.
•  A laboratory thermometer is used in labs, has a range of –10°C to 110°C, and has no kink.

5. Units of temperature

•  Degree Celsius (°C) is commonly used in India.
•  Degree Fahrenheit (°F) is used in some countries.

6. Transfer of heat

•  Heat always flows from a hot object to a cold object until both reach the same temperature.

7. Modes of transfer of heat

•  Conduction transfers heat through solids without movement of particles, and metals like copper and iron are good conductors.
•  Wood, plastic, and rubber are insulators and do not allow heat to pass easily.
•  Convection transfers heat in liquids and gases, and in convection particles move.
•  Boiling water shows convection, and sea breeze and land breeze occur due to convection.
•  Radiation transfers heat without any medium and can occur in vacuum.
•  Heat from the Sun reaches the Earth by radiation.

8. Conductors and insulators

•  Conductors allow heat to pass easily, while insulators do not.
•  Cooking utensils are made of metals, and their handles are made of wood or plastic for safety.

9. Sea breeze and land breeze

•  During daytime, land heats faster, warm air rises, and cool air moves from sea to land as sea breeze.
•  During night, sea cools slowly, and air moves from land to sea as land breeze.

10. Dark-coloured and light-coloured objects

•  Dark-coloured objects absorb more heat, while light-coloured objects reflect more heat.
•  White clothes are preferred in summer, and dark clothes are used in winter.

11. Why woollen clothes keep us warm

•  Wool traps air, and air is a poor conductor of heat.
•  Trapped air prevents body heat from escaping, keeping us warm.

12. Effect of heat

•  Heat causes rise in temperature and expansion of substances.
•  Heat can change the state of matter, like solid to liquid or liquid to gas.

13. Important keywords with simple definitions

•  Heat – a form of energy that makes objects hot.
•  Temperature – measure of hotness or coldness.
•  Thermometer – instrument used to measure temperature.
•  Conduction – transfer of heat through solids.
•  Convection – transfer of heat in liquids and gases.
•  Radiation – transfer of heat without any medium.
•  Conductor – substance that allows heat to pass easily.
•  Insulator – substance that does not allow heat to pass easily.

Understanding NCERT Class 7 Science Chapter 4 – Heat is important to learn how heat affects substances and how it is transferred. The chapter clearly explains conduction, convection, and radiation with daily-life examples.

These concepts are frequently asked in school examinations and are useful for foundation-level science preparation. Students should next read Chapter 5: Acids, Bases and Salts to understand basic chemical nature of substances used in daily life.

FAQs

Q1. What is explained in NCERT Class 7 Science Chapter 4?
The chapter explains heat, temperature, thermometers, and transfer of heat.

Q2. What is the difference between heat and temperature?
Heat is a form of energy, while temperature measures hotness or coldness.

Q3. What are the modes of transfer of heat?
The three modes are conduction, convection, and radiation.

Q4. Why do woollen clothes keep us warm?
Wool traps air, which is a poor conductor of heat and prevents loss of body heat.

Q5. Why is NCERT Class 7 Science Chapter 4 important for exams?
It explains basic heat concepts and daily-life applications that are commonly asked in exams.

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