Correct statement about `heat` and `work` is that

Options

A. Heat appears at surface only and work in bulk
B. Heat appears in bulk and work only at surface
C. Both heat and work appear in bulk of sysem
D. Both heat and work appear on surface only

Answer

To determine the correct statement about heat and work, we need to analyze the definitions and characteristics of both concepts in thermodynamics.

### Step-by-Step Solution:

1. **Understanding Heat and Work**:
- Heat is defined as the transfer of thermal energy between systems due to a temperature difference. It can occur at the surface of a system where thermal interactions take place.
- Work, on the other hand, is the transfer of energy that results from a force acting over a distance. It can occur in the bulk of the system, such as when a gas expands against a piston.

2. **Analyzing the Options**:
- **Option A**: "Heat appears at a surface only and work in bulk."
- This statement suggests that heat transfer occurs at the surface of a system, while work can occur throughout the bulk of the system.
- **Option B**: "Heat appears in bulk and work only at surface."
- This statement is incorrect because heat transfer does not occur in bulk; it occurs at the surface.
- **Option C**: "Both heat and work appear in bulk of system."
- This statement is also incorrect since heat transfer is primarily a surface phenomenon.
- **Option D**: "Both heat and work appear on surface only."
- This statement is incorrect because work can occur in the bulk of the system.

3. **Conclusion**:
- Based on the definitions and the analysis of the options, the correct statement is **Option A**: "Heat appears at a surface only and work in bulk."

### Final Answer:
The correct statement about heat and work is: **A. Heat appears at a surface only and work in bulk.**