Photo-electric emission is observed from a metalli surface for frequenceis `f_(1)` and `f_(2)` of the incident light. `(f_(1)gtf_(2))` .If the maximum values of K.E. of photo-electrons emitted in two cases are in the ratio 1:n, then the threshold frequency of a metallic surface is .......

Options

A. `(f_(1)-f_(2))/(n-1)`
B. `(nf_(1)-f_(2))/(n-1)`
C. `(nf_(2)-f_(1))/(n-1)`
D. `(f_(1)-f_(2))/(n)`

Answer

B

Explanation

`therefore K_(1)=h(f_(1)-f_(0))` and `K_(2)=h(f_(2)-f_(0))`
`therefore (K_(2))/(K_(1))=(f_(2)-f_(0))/(f_(1)-f_(0))`
`therefore (K_(2))/(K_(1))=(f_(2)-f_(0))/(f_(1)-f_(0))`
`therefore (nK_(1))/(K_(1))=(f_(2)-f_(0))/(f_(1)-f_(0))`
`therefore nf_(1)-nf_(0)=f_(2)-f_(0)`
`therefore nf_(1)-f_(2)=(n-1)f_(0)`
`therefore f_(0)=(nf_(1)-f_(2))/(n-1)`