An ultraviolet light of wavelength 2000 Å irradiates a photo cell made of molybdenum metal . If the stopping potential is `-1.5`V , what is the work function of the metal ?

Options

A. `2.5 xx 10^(-19)J`
B. `5.0 xx 10^(-19)J`
C. `7.5 xx 10^(-19)J`
D. `1 xx 10^(-18)J`

Answer

C

Explanation

Frequency of incident radiation is
`upsilon=c/lamda=(3xx10^8 )/(2000xx10^(-10))=1.5 xx10^(15)Hz`
The work function of the metal is
`phi_(0) = hupsilon-eV_s`
`= 6.6 xx 10^(-34) xx 1.5 xx 10^(15) -1.6 xx 10^(-19) xx 1.5 = 7.5 xx10^(-19) J`