Question

If the wavelength of light in an experiment on photoelectric effect is doubled,
(a) photoelectric emission will not take place
(b) photoelectric emission may or may not take place
(c) the stopping potential will increase
(d) the stopping potential will decrease

Answer 1

(b) photoelectric emission may or may not take place
(d) the stopping potential will decrease

For photoelectric effect to be observed, wavelength of incident light should not be more than the largest wavelength called threshold wavelength $\left({\lambda }_0\right)$. If the wavelength of light in an experiment on photoelectric effect is doubled and if it is equal to or less than the threshold wavelength, then photoelectric emission will take place. If it is greater than the threshold wavelength, photoelectric emission will not take place. The photoelectric emission may or may not take place.Photoelectric emission depends on the wavelength of incident light.

Hence, option (b) is correct and (a) is incorrect.

From Einstein's photoelectric equation,
$e{V}_0=\frac{hc}{{\lambda }_0}-\phi$,
where V₀ = stopping potential
${\lambda }_0$ = threshold wavelength
h = Planck's constant
$\phi$ = work-function of metal
It is clear that
$V_0\propto \frac{1}{{\lambda }_0}$
Thus, if the wavelength of light in an experiment on photoelectric effect is doubled, its stopping potential will become half.