Ultraviolet beam of wavelength 280 nm is incident on lithium surface of work function 2.5 eV. The maximum velocity of electron emitted from metal surface is

Options

A. `8.2 xx 10^(5) m//s`
B. ` 10^(6) m//s`
C. `7 xx 10^(5) m//s`
D. `6 xx 10^(5) m//s`

Answer

A

Explanation

According to Einstein.s photoelectric equation
`(hc)/lamda = phi_(0) +1/2 mv_("max")^2`
`:. v_(max ) =sqrt((2((hc)/lamda-phi_0))/m)=sqrt((2((1240)/(280)-2.5))/(9.1xx10^(-31)))`
(Using hc = 1240 eV nm)
`=sqrt(((2xx1.9 xx1.6 xx10^(-19))/(9.1xx10^(-31)))) =8.2 xx10^(5 ` m/s