Light of wavelength `lamda` strikes a photoelectric surface and electrons are ejected with kinetic energy K. If K is to be increased to exactly twice its original value, the wavelength must be changed to `lamda'` such that

Options

A. `lambda^(') lt lambda//2`
B. `lambda^(') gt lambda//2`
C. `lambda gt lambda^(') gt lambda//2`
D. `lambda^(') = lambda//2`

Answer

C

Explanation

`(hc)/lambda^(.) = 2epsilon + phi`
`(hc)/(lambda) lt 1`, So `lambda^(.) lt lambda`
Also, `lambda^(.)/lambda =1/2 [(epsilon + phi)/(epsilon + phi/2)]`
`lambda^(.)/lambda gt 1/2` or `lambda gt lambda^(.) gt lambda/2`