Which of the following statement is correct

Options

A. Good emitter are bad absorber
B. Good electrical conductor is also a good thermal conductor and vice-versa always
C. Good electrical conductor is also a good thermal conductor but good thermal conductors need not be good electrical conductors
D. Good absorbers are good reflector

Answer

To solve the question regarding which statement is correct, we will analyze each statement one by one based on the principles of thermal conduction and radiation.

### Step-by-Step Solution:

1. **Analyze Statement 1: "Good emitters are bad absorbers."**
- According to Kirchhoff's Law of Thermal Radiation, the emissive power (E) of a body is directly related to its absorptive power (A) at thermal equilibrium. This means that a good emitter is also a good absorber.
- Therefore, this statement is **incorrect**.

2. **Analyze Statement 2: "Good electrical conductors are also good thermal conductors and vice versa always."**
- It is true that good electrical conductors (like copper) are generally good thermal conductors due to the presence of free electrons that facilitate both electrical and thermal conduction.
- However, the reverse is not always true. For example, diamond is a good thermal conductor but a poor electrical conductor.
- Hence, this statement is **incorrect**.

3. **Analyze Statement 3: "Good electrical conductors are also good thermal conductors but good thermal conductors need not be good electrical conductors."**
- This statement aligns with our understanding of materials. Good electrical conductors (like metals) are typically also good thermal conductors. However, there are exceptions where materials are good thermal conductors but not good electrical conductors (like diamond).
- Therefore, this statement is **correct**.

4. **Analyze Statement 4: "Good absorbers are good reflectors."**
- This statement contradicts the principle of energy absorption and reflection. A good absorber of energy will absorb most of the energy incident on it and will not reflect much. Thus, a good absorber cannot be a good reflector.
- Therefore, this statement is **incorrect**.

### Conclusion:
The only correct statement among the given options is **Statement C**: "Good electrical conductors are also good thermal conductors but good thermal conductors need not be good electrical conductors."

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