Question

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?

Solution

Correct option is

2.0 V

If W be the work function of the surface and v the frequency of light falling on the surface, then according to Einstein’s photoelectric equation, the maximum kinetic energy of the electrons emitted from the surface is given by

          

If  be the wavelength of the light and c the speed, then 

        

Here, 

   

        

          

And,  

   

        

  

            

            

Suppose the stopping potential is V0. Then    

          

Where,  (electronic charge). Hence, the stopping potential is  

        

             

              = 2.0 V.

SIMILAR QUESTIONS

Q1

The wavelength of a photon is 1.4 Å. It becomes 2.0 Å after a collision with an electron. Calculate the energy of the scattered electron. 

  

Q2

Find the moment and equivalent mass of a photon of radiation of wavelength 3300 Å. 

Q3

An isolated hydrogen atom emits a photon of energy 10.2 eV. Calculate momentum of the photon. 

Q4

Light of wavelength 3500 Å is incident on two metals A and B. Which metal will emit photoelectrons, if their work functions are 4.2 eV and 1.9 eV respectively? 

Q5

A light beam of wavelength 6000 Å and intensity  falls normally on a photon-cathode of surface area 1 cm2 and work function 2 eV. Assuming that there is no loss of light by reflection etc., calculate the number of photoelectrons emitted per second. 

Q6

When a beam of 10.6-eV photons of intensity 2.0 Wm–2 falls on a platinum surface of area  and work function 5.6 eV, 0.53% of the incident photons eject photoelectrons. Find the number of photoelectrons emitted per second and their minimum and maximum energies (in eV). Take . 

Q7

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

Q8

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 

Q9

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. 

Q10

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