A light wave described by (in SI units) falls on a metal surface of work function 2.8 eV. The maximum kinetic energy of ejected photoelectron is (approximately) ______ eV.

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Solution

Q.
A light wave described by $E = 60 [\sin (3 \times 10^{15}) t + \sin (12 \times 10^{15}) t]$ (in SI units) falls on a metal surface of work function 2.8 eV. The maximum kinetic energy of ejected photoelectron is (approximately) ______ eV. $(h = 6.6 \times 10^{- 34} J·s and e = 1.6 \times 10^{- 19} C)$ [2026]

1 7.8

2 3.8

3 5.1

4 6.0

Ans.
(3)

$ω_{1} = 3 \times 10^{15} rad/sec$

$ω_{2} = 12 \times 10^{15} rad/sec$

$∵ ν = \frac{ω}{2 π}$

$E_{photon} = h ν = 6.6 \times 10^{- 34} \times 1.91 \times 10^{15}$

$= 1.26 \times 10^{- 18} J$

$E_{\max} = \frac{1.26 \times 10^{- 18}}{1.6 \times 10^{- 19}} \approx 7.9 eV$

$K_{\max} = E_{\max} - ϕ_{0}$

$= 7.9 - 2.8$

$K_{\max} = 5.1 eV$

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