A 5 watt source emits monochromatic light of wavelength 5000Å. When placed 0.5 
away, it liberates photoelectrons from a photosensitive metallic surface. When the source is moved to a distance of 1.0 
, the number of photoelectrons liberated will be reduced by a factor of
Text Solution
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For a light source of power 
watt, the intensity at a distance 
is given by 
where we assume light to spread out uniformly in all directions i.e., it is a spherical source.
or 
or, 
or, 
or, 
In a photoelectric emission, the number of photoelectrons liberated per second from a photosensitive metallic surface is proportional to the intensity of the light. When a intensity of source is reduced by a factor of four, the number of photoelectrons is also reduced by a factor of 4.
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