State the method by which heat is transferred :
from the bottom of a hot liquid to its upper cooler parts.

Answer

To determine the method by which heat is transferred from the bottom of a hot liquid to its upper cooler parts, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Heat Transfer**: Heat transfer occurs in three main ways: conduction, convection, and radiation. In this scenario, we are focusing on how heat moves within a liquid.

2. **Identifying the Liquid**: When we heat a liquid, such as water, from the bottom, the molecules at the bottom gain energy and start to move faster.

3. **Effect of Heating**: As the bottom molecules gain heat, their temperature increases, causing them to become less dense. This decrease in density allows these heated molecules to rise to the top of the liquid.

4. **Movement of Cooler Molecules**: As the hot molecules rise, they leave behind cooler, denser molecules at the top. These cooler molecules then move down to take the place of the rising hot molecules.

5. **Formation of a Cycle**: This movement creates a continuous cycle where hot water rises to the top while cooler water descends to the bottom. This process of circulating fluid is known as convection.

6. **Conclusion**: Therefore, the method by which heat is transferred from the bottom of a hot liquid to its upper cooler parts is called convection.

### Final Answer:
**Convection** is the method by which heat is transferred from the bottom of a hot liquid to its upper cooler parts.

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