Question

Assuming photoemission to take place, the factor by which the maximum velocity of the emitted photoelectrons changes when the wavelength of the incident radiation is increased by four times is
[Haryana CEE 1996]

• A. 4
• B. $\frac{1}{4}$
• C. 2
• D. $\frac{1}{2}$

Answer 1

The correct option is D $\frac{1}{2}$

$\frac{hc}{\lambda }=W_0+\frac{1}{2}m{v}_{max}^2$
Assuming $W_0$ to be negligible in comparison to $\frac{hc}{\lambda }$

$i.e.v_{max}^2\infty \frac{1}{\lambda }\Rightarrow v_{max}\infty \frac{1}{\sqrt{\lambda }}.$

(On increasing wavelength $\lambda to4\lambda ,v_{max}$ becomes half).