A 5 watt source emits monochromatic light of wavelength 5000 A ˚ . When placed 0.5 m away, it liberates photoclectrons from a photosensitive metallic surface. When the source is moved to a distance of 1.0 m , the number of photoelectrons liberated will be reduced by a factor of :

Question

A 5 watt source emits monochromatic light of wavelength 5000 A ˚ . When placed 0.5 m away, it liberates photoclectrons from a photosensitive metallic surface. When the source is moved to a distance of 1.0 m , the number of photoelectrons liberated will be reduced by a factor of :, 8, 16, 2, 4

MARKS App · Accepted Answer

Intensity is given by I = 4 π d 2 p ​ where p = power of source d = distance We know (assume) that light to spread out uniformly is all direction i.e. spherical source. ​ ∴ I ∝ d 2 1 ​ or I 2 ​ I 1 ​ ​ = d 1 2 ​ d 2 2 ​ ​ or I 2 ​ I 1 ​ ​ = ( 0.5 1 ​ ) 2 ⇒ I 2 ​ I 1 ​ ​ = 4 or I 2 ​ = 4 I 1 ​ ​ ​

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