When light of wavelenght `lambda` incident on a metal then stopping potential is 10V. If wavelengt is increase to `3 lambda` then stopping potential is 2V . Which of the following can emit electron form the metal : -

Options

A. ` 5 lambda `
B. `7 lambda`
C. `9 lambda`
D. `10 lambda`

Answer

A

Explanation

(e ) (10)` = (hc)/(lambda) - (hc)/(lambda_(Th)) ………(i)`
(e ) `(2) = (hc)/(3lambda) - (hc)/(lambda_(Th))…….(ii)`
`((i))/((ii)) rArr 5 =((hc)/(lambda) - (hc)/(lambda))/((hc)/(lambda) - (hc)/(lambda_(Th)))`
` rArr (5)/(3lambda) - (5)/(lambda_(Th)) = (1)/(lambda) - (1)/(lambda_(Th))`
`rArr (2)/(3lambda) = (4)/(lambda_(Th))`
`rArr lambda_(Th) = 6 lambda`