Question

Use Einstein's photoelectric equation to show how from this graph,
(i) Threshold frequency, and
(ii) Planck's constant can be determined.

Answer 1

Einstein's photoelectric equation is (K. E.)_max = hv - W

⇒ (K. E.)_max = hv - W = eV_s

⇒ eV_s = hv - W

⇒ `"V"_s = "h"/"e" "v" - "w"/"e""`

⇒ y = mx + c

As we can see a graph can be plotted between stopping potential and frequency of incident photons.

(i) Threshold frequency can be obtained from the graph where the graph cuts the x-axis, i.e. where the value of stopping potential becomes zero. 

(ii) As the slope of the graph is `"h"/"e"`, hence by calculating the slope and multiplying it by the value of charge 'e' we can also find the value of plank's constant.