A metal surface is illuminated by light of two different wavelengths 248 nm and 310 nm. The maximum speeds of the photoelectrons corresponding to these wavelengths are `u_1` and `u_2` respectively. If the ratio `u_1: u_2 = 2:1 and hc= 1240 eV` nm, the work function of the metal is neraly. (a)3.7 eV (b) 3.2 eV (c ) 2.8eV (d) 2.5eV.

Options

A. `3:7 eV`
B. `3.2 eV`
C. `2.8 eV`
D. `2.5 eV`

Answer

A

Explanation

`248 nm=1240//248 ev-= 5ev`
`310nm -=1240//310ev=4 ev`
`(K.E_(1))/(K.E_(2))=(4)/(1)=(5ev-W)/(4ev-W)`
`rArr 16-4W=S-W`
`rArr11-3W`
`rArrW=(11)/(3)=3.67 ev ~=3.7 ev`