Transfer of heat: Conduction & Convection - Class 7

Class 7, Chapter 4- Heat, Lesson- 3

1. Transfer of heat: Conduction & Convection Suman Kumar Krishna Integrated B.Sc. B.Ed. (Medical)

2. Heat flows from a body at a higher temperature to a body at a lower temperature. This is called transfer of heat. Heat is transferred in three different ways. They are :- i) Conduction ii) Convection iii) Radiation TRANSFER OF HEAT

3. Conduction Conduction is the transfer of heat from a hotter part to a colder part of an object due to the collision of its particles without actual movement of the particles from their position.

4. CONDUCTORS AND INSULATORS Conductors :- Conductors are materials which allow heat to pass through them easily. E.g. :- iron, aluminum, copper etc . Insulators :- Insulators are materials which do not allow heat to pass through them easily. E.g. :- wood, plastic, glass, rubber, air, water etc.

5. Just think: W ill heat be transferred if temperature of two objects are the same.

6. Convection The transfer of heat in liquids and gases is called Convection. The molecules of the liquid or gases that are near the source of the heat get heated first. They become lighter due to the heat and move upwards. The colder particles being heavier take the place and this process continues until the whole liquid or the gas gets heated. That is why the area above the flame of a candle always feels hot but the area on the sides of the candle does not.

7. Air is a very poor conductor of heat, Air transfers heat from its hotter parts to the colder parts by the process of convection. Convection in Air

8. Water is a poor conductor of heat. So, due to this reason, it cannot transfer heat by conduction but it transfers heat by the process of convection. Convection in Water

9. What would happen if there is no conduction of heat ? What would happen if all object around us become good conductor of heat ? What things that you see in your surrounding which is related to convection of heat?

10. Choose the Correct Option: Transfer of heat happens: - hot to cold cold to hot hot to hot cold to cold

11. State True or False: The materials which allow heat to pass through them easily are conductors of heat. [True/ False]. The water and air are poor conductors of heat. [ True/ False].

12. So, today we have learnt about ‘ Transfer of heat: Conduction & Convection ’ and now let’s summarize today’s class:  Define the term Conduction of heat and Convection of heat.  Tell one example of conduction of heat and one of convection of heat.  Name two types of heat transfer.  State a difference between conductor of heat and insulator of heat.

13. Homework Take a sheet of paper. Draw a spiral on it as shown in the Fig. Cut out the paper along the line. Suspend the paper as shown in Fig. 4.14 above a lighted candle. Observe what happens. Think of an explanation