Er. Happy Sharma
Physics Class VII
Chapter 7: Heat Transfer in Nature
Introduction
Heat transfer is an essential concept in physics that describes how thermal energy
moves from one place to another. In nature, heat transfer happens in three main ways:
conduction, convection, and radiation. These processes help us understand everyday
events like why the weather changes, how ocean currents flow, and how the water cycle
works. By studying heat transfer, we can explain why some materials feel hot or cold
and how heat a ects the world around us.
7.1 Conduction of Heat
Conduction is one way heat moves through materials. It happens mostly in solids when
particles touch each other and pass heat along.
Definition: Conduction is the process where heat energy transfers through direct
contact between particles of a substance, usually in solids.
In solids like metals, particles are close together, so heat moves quickly. In
materials like wood or air, particles are farther apart, so heat moves slowly.
Activity 7.1: Let us experiment
This activity shows how heat travels through a metal strip by conduction.
,Er. Happy Sharma
Materials Needed: A metal strip (such as aluminium or iron, about 15 cm long),
four pins, wax, a candle or spirit lamp, a stand.
Procedure:
1. Take the metal strip and use wax to attach four pins along its length.
Space the pins equally, about 2 cm apart.
2. Clamp one end of the metal strip to a stand so it stays in place.
3. Light the candle or spirit lamp and heat the free end of the metal strip.
4. Watch carefully and note the order in which the pins fall as the wax melts.
Observations:
o The pin closest to the heated end falls first because it gets hot first.
o The next pin falls second, then the third, and the pin farthest from the heat
falls last.
o This shows that heat moves through the metal from the hot end to the
cooler end.
Conclusion: Metals are good at conducting heat because they allow heat energy
to pass through them easily.
Table 7.1: Falling of pins
This table records the order in which pins fall and explains why.
Pin falling first Prediction Observation Reasons for what you observed
Pin I Falls first Falls first It is closest to the heat source.
, Er. Happy Sharma
Pin falling first Prediction Observation Reasons for what you observed
Pin II Falls second Falls second It is next in line from the heat source.
Pin III Falls third Falls third It is farther from the heat source.
Pin IV Falls last Falls last It is farthest from the heat source.
Table 7.2: List of good or poor conductors of heat
This table lists materials and whether they conduct heat well or poorly.
S.No. Material Good or Poor conductor of heat
1. Steel Good conductor
2. Wood Poor conductor
3. Air Poor conductor
4. Copper Good conductor
5. Glass Poor conductor
Definition: Materials like metals that allow heat to pass through them easily are called
good conductors of heat. Because metals are good conductors of heat, we use utensils
made of metals for cooking. In solids, heat transfer takes place mainly through the
process of conduction.
Definition: Materials such as glass and wood do not allow heat to pass through them
easily and are poor conductors (insulators) of heat. Clay and porcelain are also poor
conductors of heat — that is why tea or co ee kept in such cups stays hot longer.
Applications of conduction: During winters, we prefer wearing woollen clothes to keep
ourselves warm. Woollen fabric traps air in its pores and as air is a poor conductor of
heat, it reduces heat flow from our bodies to our surroundings. As a result, we feel
warm.
Physics Class VII
Chapter 7: Heat Transfer in Nature
Introduction
Heat transfer is an essential concept in physics that describes how thermal energy
moves from one place to another. In nature, heat transfer happens in three main ways:
conduction, convection, and radiation. These processes help us understand everyday
events like why the weather changes, how ocean currents flow, and how the water cycle
works. By studying heat transfer, we can explain why some materials feel hot or cold
and how heat a ects the world around us.
7.1 Conduction of Heat
Conduction is one way heat moves through materials. It happens mostly in solids when
particles touch each other and pass heat along.
Definition: Conduction is the process where heat energy transfers through direct
contact between particles of a substance, usually in solids.
In solids like metals, particles are close together, so heat moves quickly. In
materials like wood or air, particles are farther apart, so heat moves slowly.
Activity 7.1: Let us experiment
This activity shows how heat travels through a metal strip by conduction.
,Er. Happy Sharma
Materials Needed: A metal strip (such as aluminium or iron, about 15 cm long),
four pins, wax, a candle or spirit lamp, a stand.
Procedure:
1. Take the metal strip and use wax to attach four pins along its length.
Space the pins equally, about 2 cm apart.
2. Clamp one end of the metal strip to a stand so it stays in place.
3. Light the candle or spirit lamp and heat the free end of the metal strip.
4. Watch carefully and note the order in which the pins fall as the wax melts.
Observations:
o The pin closest to the heated end falls first because it gets hot first.
o The next pin falls second, then the third, and the pin farthest from the heat
falls last.
o This shows that heat moves through the metal from the hot end to the
cooler end.
Conclusion: Metals are good at conducting heat because they allow heat energy
to pass through them easily.
Table 7.1: Falling of pins
This table records the order in which pins fall and explains why.
Pin falling first Prediction Observation Reasons for what you observed
Pin I Falls first Falls first It is closest to the heat source.
, Er. Happy Sharma
Pin falling first Prediction Observation Reasons for what you observed
Pin II Falls second Falls second It is next in line from the heat source.
Pin III Falls third Falls third It is farther from the heat source.
Pin IV Falls last Falls last It is farthest from the heat source.
Table 7.2: List of good or poor conductors of heat
This table lists materials and whether they conduct heat well or poorly.
S.No. Material Good or Poor conductor of heat
1. Steel Good conductor
2. Wood Poor conductor
3. Air Poor conductor
4. Copper Good conductor
5. Glass Poor conductor
Definition: Materials like metals that allow heat to pass through them easily are called
good conductors of heat. Because metals are good conductors of heat, we use utensils
made of metals for cooking. In solids, heat transfer takes place mainly through the
process of conduction.
Definition: Materials such as glass and wood do not allow heat to pass through them
easily and are poor conductors (insulators) of heat. Clay and porcelain are also poor
conductors of heat — that is why tea or co ee kept in such cups stays hot longer.
Applications of conduction: During winters, we prefer wearing woollen clothes to keep
ourselves warm. Woollen fabric traps air in its pores and as air is a poor conductor of
heat, it reduces heat flow from our bodies to our surroundings. As a result, we feel
warm.
