Two sources emit beams of light of wavelength 550 nm.The light from source A has an intensity of 10 µW/m²,and the light from source B has an intensity of 20 µW/m².This is all we know about the two beams.Which of the following statements about these beams are correct? (There could be more than one correct choice. ) A)Beam B carries twice as many photons per second as beam A. B)A photon in beam B has twice the energy of a photon in beam A. C)The frequency of the light in beam B is twice as great as the frequency of the light in beam A. D)A photon in beam B has the same energy as a photon in beam A. E)None of the above statements are true.

Question

Quizplus · Accepted Answer

Intensity is proportional to the number of photons emitted per unit time per unit area. 
Let the number of photons emitted per second by A be N_A and that by B be N_B. 
Then, 
10 µW/m² = N_A * hc/λ 
20 µW/m² = N_B * hc/λ 
Dividing the second equation by the first, we get: 
2 = N_B/N_A 
So, beam B carries twice as many photons per second as beam A (Option A is correct).

Energy of a photon is given by E = hc/λ. 
Since the wavelength of both beams is the same, the energy per photon is also the same for both beams. So, Option B and D are incorrect.

Frequency is given by f = c/λ, where c is the speed of light. 
Since the wavelength of both beams is the same, the frequency is also the same for both beams. So, Option C is incorrect.

Therefore, the only correct statement is Option A.

Two Sources Emit Beams of Light of Wavelength 550 Nm