Four identical copper balls are painted blue, red, black, and white. After heating them to the same temperature, the one which cools fastest is the _____ ball.

Options

A. red
B. black
C. white
D. blue

Answer

To determine which of the four identical copper balls (painted blue, red, black, and white) cools the fastest after being heated to the same temperature, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Heat Absorption and Emission:**
- Different colors absorb and emit heat differently. Darker colors tend to absorb more heat and also emit heat more effectively than lighter colors.

2. **Identifying the Properties of Colors:**
- The black ball is a good absorber of heat. According to physics, a good absorber of heat is also a good emitter of heat. This means that the black ball will not only absorb heat quickly but will also lose heat quickly.

3. **Applying Kirchhoff's Law:**
- Kirchhoff's law of thermal radiation states that a good absorber of heat is also a good emitter of heat. Thus, since the black ball absorbs heat well, it will also emit heat rapidly.

4. **Comparing the Balls:**
- The other balls (blue, red, and white) will not cool as fast as the black ball because they are lighter in color and do not emit heat as effectively as the black ball.

5. **Conclusion:**
- Therefore, after heating the four balls to the same temperature, the black ball will cool the fastest.

### Final Answer:
The ball that cools the fastest is the **black ball**.

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