Question

Which mode of heat transfer is dominant in vacuum?

• A. Conduction
• B. Convection
• C. Radiation
• D. All are equal

Hint:

Radiation follows the Stefan-Boltzmann Law: \( Q = \sigma A T^4 \).
Notice that heat transfer by radiation is highly dependent on the absolute temperature (raised to the power of 4).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
There are three primary modes of heat transfer: conduction, convection, and radiation.
- Conduction requires a physical medium (solid, liquid, or gas) and occurs through molecular vibration or free electron movement.
- Convection requires a fluid medium (liquid or gas) and occurs through the bulk motion of the fluid.
- Radiation occurs via electromagnetic waves and does not require any material medium.
Step 2: Detailed Explanation:
A vacuum is a space devoid of matter.
Since conduction and convection rely on the presence of atoms/molecules to transfer energy, they cannot occur in a vacuum.
Radiation, being electromagnetic in nature (like light), can travel through empty space.
Therefore, in a vacuum environment (such as space or between the walls of a thermos flask), heat can only be transferred effectively via radiation.
Step 3: Final Answer:
Radiation is the only mode of heat transfer that can operate in a vacuum.