Light of frequency `7.21xx10^(14)Hz` is incident on a metal surface. Electrons with a maximum speed of `6.0 xx 10^(5)` m/s are ejected from the surface. What is the threshold frequency for photoemission of electrons?

Explanation

`upsilon=7.21xx10^(14)Hz, v=6xx10^(5)ms^(-1)`
`(1)/(2)mv_("max")^(2)=h(upsilon-upsilon_(0))=hupsilon-h upsilon_(0)`
`h upsilon_(0)=h upsilon-(1)/(2)mv_("max")^(2)`
`upsilon_(0)=upsilon-(1)/(2)(mv_("max")^(2))/(h)=7.21xx10^(14)-(1)/(2)xx(9.1xx10^(-31)xx(6xx10^(5))^(2))/(6.6xx10^(-34))=4.73xx10^(14)Hz`