A metal plate is exposed to light with wavelength `lambda`. It is observed that electrons are ejected from the surface of the metal plate. When a retarding uniform electric field E is imposed, no electron can move away from the plate farther than a certain distance d. Then the threshold wavelength `lambda_(0)` for the material of plate is ( e is the electronic charge, h is Planck's constant and c is the speed of light)

Options

A. `(lambdaeEd)/((eEd-hc))`
B. `(lambdahc)/(hc-eEdlambda)`
C. `(eEdlambda-hc)/(hclambda)`
D. `(lambdahc-eEd)/(hclambda)`

Answer

b

Explanation

Max K.E.=`eEd=(hc)/(lambda)-(hc)/(lambda_(0))`
or `1/(lambda_(0))=1/(lambda)-(eEd)/(hc)=(hc-eEdlambda)/(hclambda)`
or `lambda_(0)=(hclambda)/(hc-eEdlambda)`