Question

X-rays are used to irradiate sodium and copper surface in two separate experiments and stopping potential determined. The stopping potential is

• A. equal in both the cases
• B. greater for sodium
• C. greater for copper
• D. infinite in both the cases

Answer 1

The correct option is B greater for sodium

Stopping potential $e{V}_o=E_{incident}-\varphi$
where $E_{incident}$ is the energy of incident X-rays and $\varphi$ is the work function of metal surface.
Work function of sodium ${\varphi }_{Na}=2.3eV$
Work function of Copper ${\varphi }_{Cu}=4.7eV$
Thus stopping potential is greater for sodium.