Question

A copper ball of radius $1\, cm$ and work function $4.47\,eV$ is irradiated with ultraviolet radiation of wavelength $2500 \, \mathring{A}$. The effect of irradiation results in the emission of electrons from the ball. Further the ball will acquire charge and due to this there will be a finite value of the potential on the ball. The charge acquired by the ball is:

• A. $5.5\times10^{-13}C$
• B. $7.5\times10^{-13} C$
• C. $4.5\times10^{-12} C$
• D. $2.5\times10^{-11}C$

Answer 1

Answer: (A)

From photo electric effect equation : ]
$h v=h v_{0}+K . E_{\max }$
so Maximum kinetic energy will be
putting the given values in the above equation
$ K . E _{\max }= e \times V $
so $V$ will be
$ V=\frac{k \times Q}{r} $
$ :: q =5.5 \times 10^{-13} C $