Monochromatic radiation of wavelength 640.2 nm (1 nm = 10–9m) from a neon lamp irradiates a photosensitive material made of cesium or tungsten. The stopping voltage is measured to be 0.54 V. The neon surface is replaced by an iron source whose 427.2 nm line irradiates the material. Predict the new stopping voltage. 


Correct option is

1.51 V

For neon surface : 





If W be the work function of the material, then, by Einstein’s photoelectric equation  and the relation Ek = eV0, we have 





For iron source : 



and W is same as before. Now, we have 






              = 1.51 V.



The work function for cesium is 1.8 eV. Light of 5000 Å is incident on it. Calculate maximum velocity of the emitted electrons.


If photoelectrons are to be emitted from a potassium surface with a speedof , what frequency of radiation must be used? The threshold frequency for potassium is 


A sheet of silver is illuminated by monochromatic ultraviolet radiation of wavelength 1810 Å. What is the maximum energy of the emitted electrons? The threshold wavelength for silver is 2640 Å. 


The work function for the surface of aluminium is 4.2 eV. How much potential difference will be required to stop the emission of maximum-energy electrons emitted by light of 2000 Å wavelength?


What will be the wavelength of that incident light for which the stopping potential will be zero?


The threshold frequency for a metal is . Light of frequency  falls on the metal. What will be the cut-off voltage for photoelectric emission. 



The work function of caesium is 2.14 eV. Find the threshold frequency for caesium.


In an experiment on photoelectric emission, following observations were made wavelength of the incident light 


Light of wavelength 2000 Å falls on aluminium surface (work function of aluminium is .2 eV). Calculate cut-off wavelength for aluminium. Take, 



The first emission line in the atomic spectrum in the Ballmer series appears at: