Question

Four identical copper cylinders are painted. If they are all heated to the same temperature and left in the vacuum which will cool most rapidly?

• A. The one painted shiny white
• B. The one painted rough black
• C. The one painted shiny black
• D. The one painted rough white

Answer 1

The correct option is B

The one painted rough black

The explanation for the correct answer

In the case of option B,

1. The color black has the highest absorption and radiation qualities.
2. When an object absorbs all wavelengths and reflects none, it appears black or very dark.
3. Due to the fact that black absorbs all wavelengths, it absorbs more heat.
4. As a result, the cylinder with the black paint will absorb more heat.
5. The rough black paint had a lower reflection. Rough black paint will absorb more heat as a result.
6. As a result, it will cool down quickly.

The explanation for the incorrect answer

In the case of option A,

1. When an object reflects all wavelengths and nothing is absorbed, it appears white or very light.
2. There will be relatively little heat because the white reflects all wavelengths.
3. In comparison to black, white has a lower absorptivity.
4. As a result, the white-painted cylinder will not cool down as quickly.

In the case of option C,

1. As we saw in the previous scenario, black has the ability to absorb heat and cool down quickly.
2. A shiny finish will increase reflectivity, and the black shiny black cylinder will absorb less heat.
3. As a result, it will take a long time to cool down.

In the case of option D,

1. The absorption properties of white are quite low. This will also be reflective due to the dazzling white paint.
2. As a result, shiny white paint will not cool quickly.

Hence, option B is the correct answer.