The heat developed in a system is proportional to the current through it.

Options

A. It cannot be Thomson heat.
B. It cannot be Peltier heat.
C. It cannot be Joule heat.
D. It can be any of the three heats mentioned above.

Answer

To solve the problem, we need to analyze the relationship between heat developed in a system and the current flowing through it based on Joule's law of heating.

### Step-by-Step Solution:

1. **Understanding the Problem Statement**:
The problem states that the heat developed in a system is proportional to the current through it. We need to determine if this statement aligns with Joule's law.

2. **Recall Joule's Law**:
According to Joule's law, the heat (H) generated in a conductor is given by the formula:
\[ H = I^2 R t \]
where:
- \( H \) is the heat developed,
- \( I \) is the current,
- \( R \) is the resistance,
- \( t \) is the time for which the current flows.

3. **Analyzing the Proportionality**:
From Joule's law, we see that heat is proportional to the square of the current (\( I^2 \)). This means:
\[ H \propto I^2 \]
However, the question states that heat is directly proportional to the current (\( H \propto I \)).

4. **Conclusion**:
Since Joule's law indicates that heat is proportional to the square of the current, the statement in the question cannot be true if we are considering Joule heating. Therefore, the heat developed in a system cannot be simply proportional to the current.

5. **Final Answer**:
The answer is that the heat developed in a system is not directly proportional to the current according to Joule's law.