Question

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 (a) and (b) represent incident radiations of same frequency but of different intensities
• B. Curves (b) and (c) represent incident radiations of different frequencies and different intensities
• C. Curves (b) and (c) represent incident radiations of same frequency having same intensity
• D. Curves (a) and (b) represent incident radiations of different frequencies and different intensities

Answer 1

Answer: (A)

The energy of the incident photon is $hν$.
Hence frequency determines the energy of incident photons. This energy is imparted on the photosensitive surface to cause photo ejection. At the points where curve cuts the x axis, the incident photon energy is equal to the work potential of material. Hence energy, hence frequency, is same for radiation of curves $a $ & $b.$
Intensity is the measure of number of photons striking per unit time. Thus they determine the amount of photocurrent produced. Thus it is same for $b$ & $c$.