If the rest mass of a particle is zero, then its speed is:
Correct answer: A. Equal to speed light
- A. Equal to speed light
- B. Less than the speed of light
- C. Greater than the speed of light
- D. Not comparable with speed of light
Explanation
If the rest mass of a particle is zero, then its speed is the speed of light. This is because the rest mass of a particle is a measure of the inertia of the particle, and inertia is a measure of how much resistance a particle has to change its motion. A particle with zero rest mass has no inertia, and therefore it can move at the speed of light.
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Quantum theory treats electromagnetic radiation as packets of energy called photons, with energy proportional to frequency through E equals hf. The topic covers Planck's hypothesis, photon momentum, the photoelectric effect, threshold frequency, work function and wave particle duality, distinguishing quantised energy exchange from classical continuous radiation.
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