Light of wavelength 400 nm is incident on the cathode of a photocell, the stopping potential recorded is 6.0 V. If the wavelength of the incident light is increased to 600 nm, what will be the new stopping potential? 


Correct option is

4.97 V

Let W be the work function of the cathode surface, and v the frequency of light falling on the surface. Then, according to Einstein’s photoelectric equation, the maximum kinetic energy Ek of the emitted electrons is given by  



where  is the wavelength of the incident light. 

If the cut-off potential is V0, then the maximum kinetic energy of the electron, . Thus  



If the wavelength of the incident light is increased from , then the change (decrease) in the stopping potential will be 
















                 = 4.97 V.



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