1.

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 .......

Answer»

`(f_(1)-f_(2))/(n-1)`
`(nf_(1)-f_(2))/(n-1)`
`(nf_(2)-f_(1))/(n-1)`
`(f_(1)-f_(2))/(n)`

Solution :`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)`


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