Discussion Forum



1)

In a historical experiment to determine Planck's constant, a metal surface was irradiated with light of different wavelengths. The emitted photoelectron energies were measured by applying a stopping potential. The relevant data for the wavelength λ ) of incident light and the corresponding stopping potential V0 are given below.

1912202028_physics2Q.JPG

Given that c= 3x 108 ms-1 and e = 1.6x1019 C, Planck's constant  found from such an experiment is


A) $6.0\times 10^{-34}$

B) $6.4\times 10^{-34}$

C) $6.6\times 10^{-34}$

D) $6.8\times 10^{-34}$

Answer:

Option B

Explanation:

$\frac{hc}{\lambda}-\phi=eV_{0}$

$\frac{hc}{.3\times 10^{-6}}-\phi=2e$ ........i

$\frac{hc}{.4\times 10^{-6}}-\phi=1e$.........ii

Subtracting eq ii  from eq i

$hc\left(\frac{1}{0.3}-\frac{1}{0.4}\right)10^{6}=e$

$hc\left(\frac{.01}{0.12}\times 10^{2}\right)=e$

$h=.064\times 10^{-33}$

$h=6.4\times 10^{-34}$