Which of the following concepts is a method of heat transfer that does not require a material medium?

Step 1: Analyze the question We need the method of heat transfer that works without a material medium (it can occur even in a vacuum).

Step 2: Explain the concepts

• Conduction: Heat moves through a solid by particle vibrations and collisions (e.g., a metal spoon heating up in hot soup). It needs particles, so it needs a medium.
• Convection: Heat moves through fluids (liquids and gases) by the actual movement of the heated fluid (e.g., boiling water). It needs a fluid medium.
• Radiation: Heat moves as electromagnetic waves (infrared). These waves can travel through a vacuum, so no medium is needed. This is how the Sun's heat reaches the Earth through space.
• Diffusion: This is the spreading of particles from a region of high concentration to low concentration. It is not a heat transfer method, and it also requires a medium.

Step 3: Solve

• Conduction: needs a medium ✗
• Radiation: no medium needed ✓
• Diffusion: not a heat transfer method, needs a medium ✗
• Convection: needs a fluid medium ✗

Answer: B. radiation

Tip: Remember "Sun to Earth": the space between them is a vacuum, and since we still feel the Sun's heat, the transfer must be by radiation. Conduction and convection both need particles, while radiation needs none.