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

a. `(hc)/(lambda_(1)) = W + eV_(1)` (i)
`(hc)/(lambda_(2)) = W + e V_(2)` (ii)
Subtracting `(hc)/(lambda_(2)) - (hc)/(lambda_(1)) = e (V_(2) - V_(1))`
Here, `c = 3 xx 10^(8) m s^(-1)`,
`lambda_(1) = 4000 Å = 4 xx 10^(-7) m,V_(1) = 0.82 V`
` lambda_(2) = 3000 Å = 3 xx 10^(-7) m,V_(2) = 1.85 V`
`:. h xx 3 xx 10^(8) ((1)/(3 xx 10^(-7)) - (1)/(4 xx 10^(-7)))`
`= 1.6 xx 10^(-19) (1.85 - 0.82)`
or `h xx 3 xx 10^(8) (1)/(12 xx 10^(-7)) = 1.6 xx 10^(-19) xx 1.03`
Therefore. Plank's constant,
`h = (1.6 xx 10^(-19) xx 1.03 xx 12 xx 10^(-7))/(3 xx 10^(8))`
`= 6.592 xx 10^(-34) J-s`
b. No, because stopping potential does not depend idtensity of incident light.