Question

Stopping voltage of photoelectron ejected by light of wavelength $500nm$ is $1.2V$. If same metal surface is exposed to light of wavelength $400nm$ then ( take $hc=1240eV$

• A. threshold wavelength is around $970nm$
• B. stopping voltage for $400nm$ light is $1.82V$
• C. stopping voltage for $400nm$ light is less than $1.2V$
• D. work function of metal is $1.82eV$

Answer 1

Answer: (A), (B)

The correct options are
A threshold wavelength is around $970nm$
B stopping voltage for $400nm$ light is $1.82V$

$e{V}_0=\frac{hc}{\lambda }-\varphi \Rightarrow 1.2eV=\frac{1240}{500}-\varphi$

$\varphi =1.28eV$

$e{V}_0=\frac{1240}{400}-1.28\Rightarrow V_0=1.82V$

$\varphi =\frac{hc}{{\lambda }_0}\Rightarrow {\lambda }_0=\frac{1240}{1.28}nm=968.75nm$