Question

A photosensitive metallic surface has work function, h ${}_0$. If photons of energy 2h ${}_0$ fall on this surface, the electrons come out with a maximum velocity of 4 10${}^6$ m/s. When the photon energy is increased to 5h${}_0$, then maximum velocity of photo electrons will be

• A. 2 10${}^7$ m/s
• B. 2 10${}^6$ m/s
• C. 8 10${}^5$ m/s
• D. 8 10${}^6$ m/s

Answer 1

The correct option is D 8 10${}^6$ m/s

$2h{v}_0=h{v}_0+\frac{1}{2}m(4\times {10}^6{)}^2$
$5h{v}_0=h{v}_0+\frac{1}{2}m{v}^2\Rightarrow 4\times \frac{1}{2}m(4\times {10}^6)$
$=\frac{1}{2}m{v}^2\Rightarrow v=8\times {10}^{6}m/s$