Dual Nature of Radiation and Matter - Result Question 71

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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]

======= ####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]

3e0f7ab6f6a50373c3f2dbda6ca2533482a77bed:content/english/neet-pyq-chapterwise/physics/dual-nature-of-radiation-and-matter/dual-nature-of-radiation-and-matter—result-question-71.md (a) $10 metres / sec$

(b) $10^{2}$ metres $/ sec$

(c) $10^{4}$ metres $/ sec$

(d) $10^{6} metres / sec$

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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, $v \cong 10^{6} m / s$