First slide

Photo Electric Effect

Question

Photoelectric work function of a metal is 1 e V Light of wavelength $λ$ =3000 $Å$ falls on it, The photo-electrons come with velocity

Moderate

A

10 metre/sec
B

10²metre/sec
C

10⁴metre /sec
D

10⁶metre /sec

Solution

$hv = W + \frac{1}{2} {mv}^{2} or \frac{hc}{λ} = W + \frac{1}{2} {mv}^{2} Here λ = 3000 Å = 3000 \times 10^{- 10} m and W = 1 eV = 1 .6 \times 10^{- 19} joule \frac{(6 \cdot 6 \times 10^{- 34}) (3 \times 10^{8})}{3000 \times 10^{- 10}} = (1 \cdot 6 \times 10^{- 19}) + \frac{1}{2} \times (9 \cdot 1 \times 10^{- 31}) v^{2} Solving, we get v = 10^{6} m / s$

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