Transfer of heat: Land/ Sea breeze and radiation - Class 7

Class 7, Chapter 4- Heat, Lesson- 4

1. Transfer of heat: Land/ Sea breeze and radiation Suman Kumar Krishna Integrated B.Sc. B.Ed. (Medical)

2. The wind blowing from the land towards the sea is called the land breeze. During the night time, the land in the coastal areas gets cool down faster than the sea. The air above the sea is hotter than the air above the land. Therefore the air above the sea rises and the air from the land being cool flows towards the sea. This results in the land breeze. Land Breeze

3. Sea Breeze The wind blowing from the sea towards the land is called Sea Breeze . During the daytime, the land in the coastal area gets heated due to the sun's radiation. The sea also gets heated, however it takes more time to get heated up than the land. 

4. Hence the air above the land gets heated faster than the air above the sea. The hot air from the land rises above as it is lighter and the cool air from the sea being heavier takes its place. This results in the sea breeze.

5. Just think: how does the heat come to us from sun and which type of transfer of heat is involved in it and why?.

6. Radiation The mode of transfer of heat through which heat energy from a hot body to a cold body by means of heat rays without any material medium between them is known as radiation, e.g. the sun’s heat reaches the earth by the process of radiation. The sun is very far away from the earth, and there is mainly an empty space (vacuum) between the sun and the earth even, then the heat from the sun reaches the earth . This is due to the fact that the sun being extremely hot, emits invisible heat radiation (or infrared rays) in all directions.

7. These radiations travel through the vacuum between the sun and the earth at a very high speed and ultimately, reach us on the earth. Therefore , we can say that the transfer of heat from a hot object to a cold object by the process of radiation does not require any medium.

8. Woollen clothes are obtained from animal fibers. Woollen clothes are generally dark in color and are worn in the winter season as they protect us from the cold environment. Cotton clothes are obtained from the plant fibers. The cotton clothes are generally light in color and are worn in summer season so that we can feel cool. CLOTHES IN WINTERS AND SUMMERS

9. In the winters, we use woolen clothes. Wool is a poor conductor of heat. Moreover, there is air trapped in between the wool fibers. This air prevents the flow of heat from our body to the cold surroundings. So, we feel warm. How woolen clothes keep us warm in winter?

10. What would happen if Air around us doesn’t move ? What would happen if sun suddenly disappears or there is no sun ? What would happen if you are made to wear woolen clothes in summer and cotton clothes in winter?

11. Choose the Correct Option: Breeze that blows from the massive water bodies are termed as: - Sea Breeze Land Breeze Desert Breeze Air Breeze

12. State True or False: The transfer of heat by radiation does not require any medium. [True/ False]. From the sun heat comes to us by another process known as radiation. [True/ False].

13. So, today we have learnt about ‘ Transfer of heat: Land/ Sea Breeze and Radiation ’ and now let’s summarize today’s class :  Define the term convection of heat and heat radiation.  Tell one example of convection of heat and one of heat radiation.  Tell one difference between sea breeze and land breeze.  Explain why do we use light color umbrella in summer.

14. Homework Wrap a thin paper strip tightly around an iron rod. Try to burn the paper with candle while rotating the iron rod continuously. Does it burn? Explain your observation.