A heat engine is a device

Options

A. Which converts mechanical energy into heat energy
B. Which converts heat energy into mechanical energy
C. absorbs heat from a sink at a lower temperature and rejects to the source at high temperature
D. none of above

Answer

To solve the question regarding the function of a heat engine, we will analyze each of the given options step by step.

### Step 1: Understand the Definition of a Heat Engine
A heat engine is a device that converts heat energy into mechanical energy. It operates between two thermal reservoirs: a hot reservoir (source) and a cold reservoir (sink).

**Hint:** Recall the basic principle of a heat engine and its role in thermodynamics.

### Step 2: Analyze Each Option
1. **Option 1:** Converts mechanical energy into heat energy.
- This statement is incorrect because a heat engine does not convert mechanical energy into heat; it does the opposite.

**Hint:** Consider the flow of energy in a heat engine.

2. **Option 2:** Converts heat energy into mechanical energy.
- This statement is correct. A heat engine takes in heat energy from the hot reservoir and converts part of it into mechanical work.

**Hint:** Think about the primary function of a heat engine.

3. **Option 3:** Absorbs heat from a sink at a lower temperature and rejects it to the source at high temperature.
- This statement is incorrect. A heat engine absorbs heat from the hot reservoir (source) and rejects some heat to the cold reservoir (sink).

**Hint:** Remember the direction of heat flow in a heat engine.

4. **Option 4:** None of these.
- Since option 2 is correct, this option is also incorrect.

**Hint:** Evaluate the correctness of all previous options before concluding.

### Step 3: Conclusion
Based on the analysis, the correct answer is **Option 2**, which states that a heat engine converts heat energy into mechanical energy.

**Final Answer:** Option 2 - Converts heat energy into mechanical energy.