Two identical photocathodes receive light of frequency `f_(1) andf_(2)` if the velocites of the photo electrons (of mass `m`) coming out are repectively `v_(1) and v_(2)` then

Options

A. `v_(1)-v_(2) =[(2h)/(m)(f_(1)-f_(2))]^(1/2)`
B. `v_(1)^(2)-v_(2)^(2) =(2h)/(m)(f_(1)-f_(2))`
C. `v_(1)+v_(2) =[(2h)/(m)(f_(1)+f_(2))]^(1/2)`
D. `v_(1)^(2)+v_(2)^(2) =(2h)/(m)(f_(1)+f_(2))`

Answer

B

Explanation

`hf_(1) =phi +(1)/(2) mv_(1)^(2)`
`hf_(2) =phi +(1)/(2) mv_(2)^(2)`
(i) - (ii) `implies h(f_(1) - f_(2)) =(1)/(2)m(v_(1)^(2) - v_(2)^(2))`
`v_(1)^(2) - v_(2)^(2) =(2h)/(m) (f_(1) - f_(2))`