Required Readings
Science in Action 7
pages 217 to 220
or
Science Focus 7
pages 226 to 228
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Did You Know?
Black is a good absorber of heat, but it is also a good radiator of heat as well. So while wearing black on a cool, bright day might keep you a little warmer, it will also cool you off faster when the sun goes down. So, if you were to buy your mom or dad a new coffee mug for their birthday, which would you buy, a black cup or a white cup? Why? |
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The movement of energy by radiation is totally unlike the other to methods of heat transfer. Think for a moment about space. By our standards here on Earth, there are no particles in space. Therefore, there can be no transfer of energy by conduction or convection.
The movement of energy by radiation does not need particles. It can travel through a vacuum. Radiation travels in waves. Light from the sun reaches us in the form of waves. On Earth, heat energy can travel in waves called infrared waves. All of us have felt the heat of the sun through a window. That's a form of radiant energy.
Heat energy is just one form of radiant energy. You have been using radiant energy all your life to do many things. We use radiant energy to communicate information. Television, radio waves and microwaves are all forms of radiant energy. Doctors use radiant energy in the form of X-rays to help injured people. But there are also forms of radiant energy that can be harmful. Ultraviolet energy from the sun can cause sun burns and skin cancer. Other forms such as gamma rays can hurt us as well.
How do the Colours of Materials Affect the Absorption of Radiant Energy
In this activity you will be using data collected from a laboratory experiment.
In this experiment, a large light bulb (right) was shone on two cylindrical containers with water inside. One of them was painted white and the other black (on left). A thermometer was inserted in each cylinder to measure the temperature of the water inside each cylinder.
The data collected is found in the table below. Your job is to graph the data in a line graph and answer the questions below.
Data Table #1
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White Cylinder
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Black Cylinder
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Time in Minutes
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Temperature °C
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Time in Minutes
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Temperature °C
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| 0 |
23 |
0 |
23 |
| 1 |
23 |
1 |
27 |
| 2 |
23 |
2 |
28 |
| 3 |
24 |
3 |
30 |
| 4 |
25 |
4 |
32 |
| 5 |
26 |
5 |
33 |
| 6 |
27 |
6 |
35 |
| 7 |
27 |
7 |
36 |
| 8 |
28 |
8 |
36 |
| 9 |
28 |
9 |
37 |
| 10 |
28 |
10 |
38 |
Interesting Fact: It takes heat 8.5 minutes to radiate from the Sun to the Earth.
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