Which one of the following processes depends on gravity ?

Options

A. Conduction
B. Convection
C. Radiation
D. None of these

Answer

To determine which process depends on gravity among conduction, convection, radiation, and none of these, we can analyze each process step by step.

### Step 1: Understanding Conduction
Conduction is the process of heat transfer through direct contact of particles. It occurs in solids where free electrons and lattice vibrations transfer energy.
- **Key Point:** Conduction does not involve movement of matter and therefore does not depend on gravity.

### Step 2: Understanding Convection
Convection is the transfer of heat through the movement of fluids (liquids and gases). It can be categorized into two types:
- **Free Convection:** This occurs due to the natural movement of fluid caused by temperature differences. For example, when a fluid is heated, it expands, becomes less dense, and rises, while cooler, denser fluid sinks. This movement is influenced by gravity.
- **Forced Convection:** This involves external forces (like fans or pumps) to move the fluid. While gravity may still play a role, the primary driving force is mechanical.

- **Key Point:** Convection relies on gravity because the movement of warmer, less dense fluid upwards and cooler, denser fluid downwards is driven by gravitational forces.

### Step 3: Understanding Radiation
Radiation is the transfer of heat in the form of electromagnetic waves. It can occur in a vacuum and does not require a medium (like air or water) to transfer heat.
- **Key Point:** Radiation does not depend on gravity, as it can occur in the absence of any medium.

### Step 4: Conclusion
Based on the analysis:
- **Conduction:** Does not depend on gravity.
- **Convection:** Depends on gravity (both free and forced convection).
- **Radiation:** Does not depend on gravity.
- **None of these:** Not applicable since convection does depend on gravity.

Thus, the process that depends on gravity is **Convection**.

### Final Answer:
**Convection** is the process that depends on gravity.

---