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The figure shows a plot of photo current versus anode potential for a photo sensitive surface for three different radiations. Which one of the following is a correct statement?
A
Curves (b) and (c) represent incident radiations of same frequencies having same intensity
B
Curves (a) and (b) represent incident radiations of different frequencies and different intensities
C
Curves (a) and (b) represent incident radiations of same frequencies but of different intensities
D
Curves (b) and (c) represent incident radiations of different frequencies and different intensities
Detailed Solution
The stopping (retarding) potential depends only on the frequency of the incident radiation: $eV_0 = h\nu - \phi_0$. Curves with the same stopping potential have the same frequency.
The saturation photocurrent depends only on the intensity of the radiation. Curves with different saturation currents have different intensities.
In the figure, curves (a) and (b) start from the same retarding potential, so they have the same frequency; their saturation currents are different, so their intensities are different.
Curve (c) starts from a different retarding potential, so its frequency is different from that of (a) and (b); hence (b) and (c) are not of the same frequency.
Hence the correct statement is that curves (a) and (b) represent incident radiations of the same frequency but of different intensities.
The saturation photocurrent depends only on the intensity of the radiation. Curves with different saturation currents have different intensities.
In the figure, curves (a) and (b) start from the same retarding potential, so they have the same frequency; their saturation currents are different, so their intensities are different.
Curve (c) starts from a different retarding potential, so its frequency is different from that of (a) and (b); hence (b) and (c) are not of the same frequency.
Hence the correct statement is that curves (a) and (b) represent incident radiations of the same frequency but of different intensities.