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`.

Explanation

Given , incident frequency , `v=7.21xx10^(14)Hz`
Maximum speed of emitted electrons , `v_(max)=6.0xx10^(5)ms ^(-1)`
Threshold frequency , `v_0` ?
Maximum kinetic energy is given by
`K_(max)=hv-hv_0`
`:. V_0=v-(K_(max))/h`
`=v-(mv_max^2)/(2h)[:.K_(max)=1/2mv_(max)""^2]`
`=7.21 xx10^(14)-((9.1xx10^(-31)xx36xx10^(10))/(2xx6.62xx10^(-34)))`
`=7.21xx10^(14)-2.47xx10^(14)`
`=4.74xx10^(14)Hz`.