Light of frequency `7.21xx10^(14)Hz` is incident on a metal surface. Electrons with a maximum speed of `6.0xx10^(5)ms^(-1)` are ejected from the surface. What is the threshold frequency for photoemission of electrons? `h=6.63xx10^(-34)Js, m_(e)=9.1xx10^(-31)kg`.

Options

A. `2.32xx10^(14)Hz`
B. `2.32xx10^(12)Hz`
C. `4.74xx10^(14)Hz`
D. `4.74xx10^(12)Hz`

Answer

C

Explanation

( c) : Here, `v=7.21xx10^(14)Hz,m_(e)=9.1xx10^(-31)kg`
`h=6.63xx10^(-34)Js,v_(max)=6xx10^(5)"m s"^(-1)`
According to Einstein's photoelectric equation
`(1)/(2)m_(e)v_(max)^(2)=hv-hv_(0) or v_(0)=v-(m_(e)v_(max)^(2))/(2h)`
`=7.21xx10^(14)-((9.1xx10^(-31))xx(6xx10^(5))^(2))/(2xx6.63xx10^(-34))`
`=7.21xx10^(14)-2.47xx10^(14)=4.74xx10^(14)Hz`