a. A stopping potential of `0.82V` is required to stop the emission of photoelectrons from the surface of a metal by light of eavelength `4000 A`. For light of wavelength `3000 A`, the stopping potential is `1.85V`. Find the value of Planck's constant. [1 electrons volt (eV)`=1.6xx10^(-19)J]`
b. At stopping potential, if the wavelength of the incident light is kept fixed at `4000 A`, but the intensity of light increases two times, will photoelectric current be botained ? Give reasons for your answer.

Explanation

(i) Here,
`lambda_1=4000Å=4xx10^-7m , V_1=0.82V,`
`lambda_2=3000Å=3xx10^-7m , V_2=1.85V,`
As `(hc)/(lambda_1)-(hc)/(lambda_1)=phi_(0)+eV_(1)` and `(hc)/(lambda_(2))=phi_(0)+eV_(2)`
`:. (hc)/(lambda_(2)) - (hc)/(lambda_(1))=e(V_(2)-V_(1))`
or `hc((lambda_1-lambda_2)/(lambda_1lambda_2))=e(V_2-V_1)`
or `h=(e(V_2-V_1)lambda_(1)lambda_(2))/((lambda_1-lambda_2)c)`
`((1.6xx10^(-19))xx(8.85-0.82)xx4xx10^-7xx3xx10^-7)/((4xx10^-7-3xx10^-7)xx3xx10^8)`
`=6.592xx10^(-34)Js`
(ii) No. because the stopping potential is independent of intensity of incident light.