The thermal conductivity of a rod depends on

Options

A. length
B. mass
C. area of cross section
D. material of the rod.

Explanation

To determine the factors on which the thermal conductivity of a rod depends, we can analyze the options provided: length, mass, area of cross-section, and material of the rod.

### Step-by-Step Solution:

1. **Understanding Thermal Conductivity**:
- Thermal conductivity (k) is defined as the ability of a material to conduct heat. It is a measure of how easily heat can pass through a material.

2. **Identifying the Nature of Thermal Conductivity**:
- Thermal conductivity is a property that characterizes the material itself. It indicates how well a material can conduct heat, regardless of its shape or size.

3. **Evaluating Length**:
- The length of the rod does not affect the thermal conductivity. For example, two rods made of the same material but of different lengths will have the same thermal conductivity value.

4. **Evaluating Mass**:
- The mass of the rod also does not influence thermal conductivity. Two rods made of the same material, regardless of their mass, will still have the same thermal conductivity.

5. **Evaluating Area of Cross-Section**:
- The area of cross-section affects the rate of heat transfer (the amount of heat transferred per unit time) but does not change the thermal conductivity value of the material itself.

6. **Evaluating Material of the Rod**:
- The thermal conductivity is fundamentally a property of the material. Different materials have different thermal conductivities. For example, metals like copper have high thermal conductivity, while materials like wood have low thermal conductivity.

7. **Conclusion**:
- Based on the analysis, the thermal conductivity of a rod depends solely on the material of the rod. Therefore, the correct answer is that the thermal conductivity depends on the **material of the rod**.

### Final Answer:
The thermal conductivity of a rod depends on the **material of the rod**.

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