When a metal plate is exposed to light of wavelength 400 nm , a negative potential of 1.1 V is found

Question

When a metal plate is exposed to light of wavelength 400 nm , a negative potential of 1.1 V is found to be needed to stop the photo current. The threshold wavelength of the photoelectrons is. $\_\_\_\_$

Professor PC Thomas Classes · Answer

Stoping potential 1.1 V
$$
\begin{array}{ll}
	ext { i.e. } K E_{\max }=1.1 \mathrm{eV} & \
h 
u=w_0+K E_{\max } & \lambda=4000 A^0 \
\frac{12400}{4000}=w_0+1.1 \mathrm{eV} & w_0=2 \mathrm{eV} \
\lambda_0=\frac{12400}{2}=6200 A^0=620 \mathrm{~nm} &
\end{array}
$$