Heat transfer that does not require a medium is called

Question

Heat transfer that does not require a medium is called

1. A. Radiation (Correct answer)
2. B. Reflection
3. C. Conduction
4. D. Convection

Correct Answer

Option A — Radiation

Detailed Solution & Explanation

The correct answer is Radiation.

Key Points

• Radiation is the mode of heat transfer that does not require any material medium — it can travel even through a vacuum.
• Heat from the Sun reaches the Earth through radiation, crossing millions of kilometres of empty space in the form of electromagnetic (infrared) waves.
• The other two modes of heat transfer both need a medium: in Conduction, heat passes through a solid by the vibration of particles without the particles themselves moving; in Convection, heat is carried by the actual movement of heated liquid or gas (as in boiling water or sea breezes).
• Reflection is not a mode of heat transfer at all — it is the bouncing back of waves from a surface.
• Hence radiation is the correct answer.

Additional Information

• The three modes: conduction needs direct contact, convection needs a fluid that can circulate, and radiation needs no medium at all — which is how solar energy crosses space.
• Radiation travels as electromagnetic waves at the speed of light, and its rate follows the Stefan-Boltzmann law, proportional to the fourth power of absolute temperature.
• A vacuum flask defeats all three at once: a vacuum stops conduction and convection, and silvered walls reflect radiation.