Fastest mode of transmission of heat is _____

Explanation

To determine the fastest mode of transmission of heat, we need to understand the three main methods of heat transfer: conduction, convection, and radiation. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Types of Heat Transfer
There are three primary modes of heat transfer:
1. **Conduction**: This is the transfer of heat through direct contact between materials. It occurs in solids where heat is transferred from one molecule to another through collisions. However, this process is relatively slow.

2. **Convection**: This mode occurs in fluids (liquids and gases) where heat is transferred by the actual movement of the fluid. For example, when a liquid is heated, the warmer, less dense parts rise while the cooler, denser parts sink, creating a convection current. This method is faster than conduction but still slower than radiation.

3. **Radiation**: This is the transfer of heat in the form of electromagnetic waves. It does not require a medium (like air or water) to transfer heat, which means it can occur even in a vacuum. An example of this is the heat from the sun reaching the Earth.

### Step 2: Compare the Speeds of Heat Transfer
- **Conduction** is the slowest mode of heat transfer because it relies on direct contact between particles.
- **Convection** is faster than conduction because it involves the movement of fluid, allowing heat to be transferred more quickly.
- **Radiation** is the fastest mode of heat transfer because it can occur through empty space and does not rely on direct contact or the movement of particles.

### Step 3: Conclusion
Based on the understanding of these three modes, we conclude that the fastest mode of transmission of heat is **radiation**.

### Final Answer
The fastest mode of transmission of heat is **radiation**.

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