If a surface has a work function 4.0 eV, what is the maximum velocity of electrons liberated from the surface when it is irradiated with ultraviolet radiation of wavelength 0.2`mum`?

Options

A. `4.4xx10^(5)ms^(-1)`
B. `8.8xx10^(7)ms^(-1)`
C. `8.8xx10^(5)ms^(-1)`
D. `4.4xx10^(7)ms^(-1)`

Answer

C

Explanation

Let us calculate energy corresponding to `0.2xx10^(-6)`m or `0.2xx10^(-6)xx10^(10)A`
or `2000A=(12375)/(2000)=6.1875 eV`
`(1)/(2)mv_(max)^(2)=(6.1875-4)eV`
or `mv_(max)^(2)=(2xx2.1875xx1.6xx10^(-19))/(9.1xx10^(-31))`
or `mv_(max)^(2)=0.769xx10^(12)=0.876xx10^(6)`
`=8.76xx10^(5)ms^(-1)`