Which heat transfer mechanism can transfer energy through space without a medium?

• A. Conduction
• B. Convection
• C. Expansion
• D. Radiation

Answer: (D)

Energy can move through space without any material in between through radiation. This means energy travels via electromagnetic waves, so a hot object can warm another object even when there is a vacuum between them—like the Sun heating Earth. Conduction requires direct contact and transfers energy through molecular interactions in a solid, while convection needs a moving fluid to carry energy; expansion is not a separate mechanism for transferring heat. All warm bodies emit radiation, and the amount depends on temperature, surface properties, and area, with higher temperatures and larger, more emissive surfaces radiating more energy.