An observer shoots parallel to a meter stick at very high (relativistic) speed and finds that the length of meter stick is________________?
Correct answer: B. less than one meter
- A. greater than one meter
- B. less than one meter
- C. one meter
- D. a foolish question
Explanation
Length contraction gives L = L0 sqrt(1 - v^2/c^2), so an object moving rapidly relative to the observer is measured shorter than its proper length of 1 m. The meter stick's own rest-frame measurement remains 1 m, but the moving observer measures less than 1 m. Students may choose c by overlooking that length depends on the frame of reference.
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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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