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Q53 (NDA-II/2019) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Thermal physics

In which of the following phenomena do heatwaves travel along a straight line with the speed of light?

Result
Your answer: —  Â·  Correct: C
Explanation

Thermal radiation is the only mode of heat transfer that occurs via electromagnetic waves. Unlike conduction and convection, which require a material medium and involve the movement of particles or bulk fluid motion, radiation can occur in a vacuum [1]. According to Maxwell's theory, these electromagnetic waves transport energy and travel at the speed of light. Because radiation consists of electromagnetic waves (specifically infrared radiation in many thermal contexts), it travels in straight lines from the source to the receiver. Conduction involves heat transfer through direct contact and molecular activity within a body, while convection involves the macroscopic movement of fluids, neither of which occurs at the speed of light or strictly in straight-line wave propagation [2]. Therefore, only thermal radiation satisfies the criteria of traveling in a straight line at the speed of light.

Sources

  1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 7: Heat Transfer in Nature > Why is it more comfortable to wear white or light-coloured clothes during summers and dark-coloured clothes during winters? > p. 97
  2. [2] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 8: Solar Radiation, Heat Balance and Temperature > HEATING AND COOLING OF ATMOSPHERE > p. 68
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