Silver has a work function of 4.7 eV. When ultraviolet light of wavelength 100 nm is incident upon it, a potential of 7.7 V is required to stop the photo electrons from reaching the collector plate. How much potential will be required to stop the photoelectrons when light of wavelength 200nm is incident upon silver?

Options

A. `15.4" eV"`
B. `2.35" V"`
C. `3.85" V"`
D. `1.5 "V"`

Answer

D

Explanation

`eV_(0)+phi=(hc)/(lambda)`
and `"eV'"_(0)+phi=(hc)/(lambda')`
`:." "("eV'"_(0)+phi)/("eV'"_(0)+phi)=(lambda)/(lambda')=(100)/(200)=(1)/(2)`
`2"eV'"_(0)+2phi=eV_(0)+phi`
`"eV'"_(0)=(eV_(0)-phi)/(2)=(7.7-4.7)/(2)=1.5" eV"`
`:." ""V'"_(0)=1.5" V"`