Light beams A and B have the same intensity but the wavelength associated with beam A is longer than that associated with beam B.The photon flux (number crossing a unit area per unit time)is:
A)greater for A than for B
B)greater for B than for A
C)the same for A and B
D)greater for A than for B only if both have short wavelengths
E)greater for B than for A only if both have short wavelengths

Question

Quizplus · Accepted Answer

The photon flux is proportional to the energy carried by each photon, which is given by E=hf, where h is Planck's constant and f is the frequency of the light. Since both A and B have the same intensity, they carry the same amount of energy per unit time. However, the photons in A have lower frequency (longer wavelength) than those in B. Therefore, each photon in A has less energy than each photon in B. As a result, in order to carry the same amount of energy per unit time, more photons must cross a unit area per unit time in A than in B. This means that the photon flux is greater for A than for B.

Light Beams a and B Have the Same Intensity but the Wavelength