Question

When a surface is irradiated with light of wavelength 4950 Å, a photocurrent appears which vanishes if a potential greater than 0.6 V is applied across the photo-table. When a different source of light is used, it is found that the critical retarding potential is changed to 1.1 V. Find the work function of the emitting surface and the wavelength of the second source. If the photoelectrons (after emission from the surface) are subject to a magnetic field of 10 T, what changes will be observed in the above two retarding potentials? 

Solution

Correct option is

1.9 eV, 4125 Å

The energy (hv1) of the light-photon incident on the surface is equal to the work function W of the surface plus the kinetic energy Ek of the emitted photoelectron.    

       

If the retarding potential is V1, then 

  

  

             

             

             

             

             = 1.9 eV. 

Using the light of another wavelength , we shall have 

        

               

             .  

  

             

             

             = 4125 Å. 

Since the magnetic field does not change the speed of the ejected electrons, there will be no change in the stopping potentials.

SIMILAR QUESTIONS

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Q5

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Q6

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Q7

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Q8

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Q9

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Q10

The maximum kinetic energy of photoelectrons emitted from a certain metallic surface is 30 eV when monochromatic radiation of wavelength  falls on it. When the sane surface is illuminated with light of wavelength , the maximum kinetic energy of photoelectrons is observed to be 10 eV. Calculate the wavelength  and determine the maximum wavelength of incident radiation for which photoelectrons can be emitted by this surface.