If a material object moves with speed of light its mass becomes ________________?
Correct answer: C. infinite
- A. equal to its rest mass
- B. double of its rest mass
- C. infinite
- D. zero
Explanation
Relativistic mass is often written m = m0/sqrt(1 - v^2/c^2), so as v approaches c, the denominator approaches zero and the mass tends to infinity. A material object with nonzero rest mass cannot actually reach light speed because that would require infinite energy. Students may choose d by incorrectly applying the zero rest mass of a photon to an ordinary material object.
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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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