Dual Nature of Radiation and Matter - Result Question 71
75. Photoelectric work function of a metal is $1 eV$. Light of wavelength $\lambda=3000 \AA$ falls on it. The photo electrons come out with velocity [1991]
«««< HEAD
======= ####75. Photoelectric work function of a metal is $1 eV$. Light of wavelength $\lambda=3000 \AA$ falls on it. The photo electrons come out with velocity [1991]
c3eec34ec6b1fad69db54a20ad4b2dca40c2aa54 (a) $10 metres / sec$
(b) $10^{2}$ metres $/ sec$
(c) $10^{4}$ metres $/ sec$
(d) $10^{6} metres / sec$
Show Answer
Answer:
Correct Answer: 75. (d)
Solution:
(d) $h v=W+\frac{1}{2} m v^{2}$ or
$\frac{h c}{\lambda}=W+\frac{1}{2} m v^{2}$
Here $\lambda=3000 \AA=3000 \times 10^{-10} m$
and $W=1 eV=1.6 \times 10^{-19}$ joule
$ \begin{aligned} & \therefore \frac{(6.6 \times 10^{-34})(3 \times 10^{8})}{3000 \times 10^{-10}} \\ & =(1.6 \times 10^{-19})+\frac{1}{2} \times(9.1 \times 10^{-31}) v^{2} \end{aligned} $
Solving we get, $v \cong 10^{6} m / s$
