# The work function for a given photosensitive surface is 2.5 eV. When light of frequency f falls on this surface, the emitted photoelectrons are completely stopped by applying a retarding potential of 4.1 V. Estimate the value of the frequency f of the light.

Since the emitted photoelectrons are completely stopped by applying a retarding potential of 4.1 V, the maximum kinetic energy of any photoelectron would be

**4.1eV**.

If the incdent light has frequency

**f**then the energy of any photon in it is

**hf**, where 'h' is Plank's constant.

From Einstein's photoelectric effect equation KE

_{max}= hf - work function

4.1ev = hf - 2.5eV

**f = 1.6 x 10**

^{15}HzRegards.

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