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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?

1. Curves (1) and (2) represent incident radiations of same frequency but of different intensities.
2. Curves (2) and (3) represent incident radiations of different frequencies and different intensities.
3. Curves (3) and (2) represent incident radiations of same frequency having same intensity.
4. Curves (1) and (2) represent incident radiations of different frequencies and different intensities.

Correct answer: Curves (1) and (2) represent incident radiations of same frequency but of different intensities.

Solution

The photoelectric current depends on the intensity of the incident radiation, while the stopping potential depends on the frequency. Since curves (1) and (2) have the same stopping potential but different saturation currents, they represent radiations of the same frequency but different intensities.

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