Suppose a liquid in a container is heated at the top rather than at the bottom. What is the main process by which the rest of the liquid becomes hot?

Explanation

To solve the question about how a liquid in a container becomes hot when heated from the top rather than the bottom, we can break down the explanation into clear steps:

### Step-by-Step Solution:

1. **Understanding Heating from the Bottom**:
- When a liquid is heated from the bottom, the heat source warms the liquid at the bottom first. As the temperature increases, the density of the liquid decreases.
- The warmer, less dense liquid at the bottom rises, while the cooler, denser liquid at the top sinks. This creates a circulation pattern in the liquid known as convection.

2. **Understanding Heating from the Top**:
- If the liquid is heated from the top, the heat is applied to the upper layer of the liquid. As this layer heats up, its density decreases.
- However, since the lighter, warmer liquid is already at the top, there is no denser liquid below it to push upward. Therefore, the typical convection currents that would distribute heat throughout the liquid do not occur.

3. **Heat Transfer Mechanism**:
- In the absence of convection (which is the case when heating from the top), the only remaining method for heat transfer in the liquid is conduction.
- Conduction is the process where heat is transferred through direct contact between molecules. The heated upper layer of the liquid will transfer heat to the layers below it through conduction.

4. **Conclusion**:
- Therefore, when a liquid is heated from the top, the main process by which the rest of the liquid becomes hot is conduction.

### Final Answer:
The main process by which the rest of the liquid becomes hot when heated from the top is **conduction**.

---