Heat Transfer in Nature – Class 7 Science notes, important questions and MCQs

Chapter overview

Heat flows from hotter to colder objects by conduction, convection and radiation. These processes explain land and sea breezes, warm clothes and much more.

Modes of heat transfer

• Conduction: through solids by contact (a metal spoon gets hot in tea).
• Convection: in liquids and gases by movement of the heated material (boiling water, sea breeze).
• Radiation: without a medium (heat from the Sun, from a fire).

Everyday examples

• Conductors (metals) and insulators (wood, plastic, air); cooking pans have plastic or wooden handles.
• Sea breeze in the day (land heats faster); land breeze at night.
• Dark colours absorb more radiation; light colours reflect it — wear light clothes in summer, woollens trap air in winter.

Key terms

Conduction

heat transfer through direct contact of particles

Convection

heat transfer by flow of a heated fluid

Radiation

heat transfer without any medium

Formulas

• Heat flows from hot to cold

Important questions with answers

Quick revision

• Solids: conduction; fluids: convection; vacuum: radiation.
• Sea breeze by day, land breeze by night.
• Dark surfaces absorb more heat.

Exam tips

• Woollen clothes keep us warm because trapped air is a poor conductor.
• The Sun's heat reaches Earth only by radiation (space has no medium).

Practice MCQs

1. Heat from the Sun reaches us by

   1. conduction
   2. convection
   3. radiation
   4. reflection only
   Show answer

   Answer: (c) radiation. No medium in space.

2. Which is a good conductor of heat?

   1. wood
   2. copper
   3. plastic
   4. cloth
   Show answer

   Answer: (b) copper. Metal.

3. A sea breeze blows during the

   1. day from sea to land
   2. night from land to sea
   3. day from land to sea
   4. night from sea to land
   Show answer

   Answer: (a) day from sea to land. Land heats faster by day.

4. Water in a pot heats up mainly by

   1. convection
   2. conduction
   3. radiation
   4. reflection
   Show answer

   Answer: (a) convection. Warm water rises.

5. Sea breeze blows during the day from

   1. land to sea
   2. mountains to plains
   3. sea to land
   4. north to south
   Show answer

   Answer: (c) sea to land. Land heats faster; air above it rises.

6. Why are light-coloured clothes preferred in summer?

   1. they are cheaper
   2. they reflect more heat
   3. they absorb more heat
   4. they are heavier
   Show answer

   Answer: (b) they reflect more heat. Less absorption.

7. Two thin blankets keep you warmer than one thick blanket of the same weight because

   1. they are softer
   2. they are heavier
   3. they absorb sunlight
   4. air trapped between them insulates
   Show answer

   Answer: (d) air trapped between them insulates. Trapped air layer.

8. Dark clothes are preferred in winter because they

   1. reflect heat
   2. absorb more heat
   3. are lighter
   4. conduct electricity
   Show answer

   Answer: (b) absorb more heat. Dark colours absorb radiation.