17. Two different sources emit beams of microwaves. All we know about the beams

Question

17. Two different sources emit beams of microwaves. All we know about the beams is that source A has a frequency of 10 GHz and source B has a frequency of 20 GHz. Which of the following must be true? A) Beam B carries twice as many photons as Beam A. B) A photon in beam B has twice the energy of a photon in Beam A. C) The intensity of beam B is twice as great as the intensity of Beam A. D) The total energy in beam B is twice as great as the total energy in beam A. E) More than one of the above must be true.

Explanation / Answer

frequency of A is fA = 10 GHz

energy of photons EA = h.fA = h. 10

frequency of B is fb = 20 GHz

enery of photons EB = h.fB = h.20

hence EB = 2 EA

i.e. A photon in beam B has twice the energy of a photon in beam A

hence answer is B

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