Upcoming SlideShare
×

# Heating And Cooling Lesson 4

2,370 views

Published on

lesson on convection of heat, year 8

0 Likes
Statistics
Notes
• Full Name
Comment goes here.

Are you sure you want to Yes No
• Be the first to comment

• Be the first to like this

Views
Total views
2,370
On SlideShare
0
From Embeds
0
Number of Embeds
9
Actions
Shares
0
43
0
Likes
0
Embeds 0
No embeds

No notes for slide

### Heating And Cooling Lesson 4

1. 1. Convection <ul><li>Target </li></ul><ul><li>To be able to explain how convection takes place in liquids and gases. </li></ul>Thursday 19 November 2009
2. 2. Experiment -What is convection? <ul><li>Observe the movement of the pink colour when water containing potassium permanganate is heated. How does the water move? Explain the movement. </li></ul>
3. 3. The purple colour from the dissolving potassium permanganate rises showing the flow of hot water in the convection current.
4. 5. Ice and boiling water in the same boiling tube! Copper wire holds the ice at the bottom of the boiling tube, the top is heated. The heat from the boiling water at the top of the tube does not reach the ice at the bottom because a convection flow of heat cannot occur.
5. 6. Convection <ul><li>Convection takes place when a hot liquid or gas at a low level rises and cold liquid or gas falls. </li></ul><ul><li>Convection does not take place in solids because the particles in a solid cannot move. </li></ul>
6. 7. Showing convection in a gas. Smoke enters the metal box, it falls in the cool air and then rises once the air is heated by the candle flame.
7. 8. Hot air balloons A hot air balloon works because the hot air inside the balloon has a lower density than the air surrounding it. We can make a simple one using a plastic bag. A real one can lift a lot of people in a basket.
8. 13. Explanation <ul><li>Hot gases or liquids have a lower density than cold gases or liquids so they rise. </li></ul><ul><li>Cold gases or liquids have a higher density so they fall. </li></ul>
9. 14. Convection versus conduction In CONDUCTION the heat was passed on by VIBRATIONS in a SOLID In CONVECTION the heat is passed on by the FLUID expanding, rising and TAKING THE HEAT with it
10. 15. Some questions on convection… <ul><li>Freezers in supermarkets are often left open to the air. Explain why the food does not melt easily. </li></ul><ul><li>Explain why a hot air balloon rises in the air. </li></ul><ul><li>Explain why an ice cube floating at the top of a drink will cool all of the drink. </li></ul>
11. 16. Question 4 <ul><li>Draw a diagram of a candle like the one shown. Add an arrow to show how heat from the flame will start a convection current. </li></ul>
12. 17. Question 5 <ul><li>Ice floats at the top of a drink. Explain how this cools the drink at the bottom of the glass. </li></ul>
13. 18. Question 6 <ul><li>Take-away containers for hot drinks usually have a lid on them. Explain why this is a good idea. </li></ul>
14. 19. Question 7 <ul><li>Copy the diagram of the hot water tank. </li></ul><ul><li>a Draw an arrow to show which way the heated water travels away from the element. Label it ‘ heated water ’ . </li></ul><ul><li>b Draw an arrow to show the flow of colder water within the tank. Label it ‘ colder water ’ . </li></ul><ul><li>c The heating element is quite close to the bottom of the tank. Why is the hot water outlet not at the bottom of the tank? </li></ul>