First slide

Photo electric effect

Question

The work function of a metal is 6.4x10^-19J. If the metal is irradiated with radiation of wavelength 200nm,then the maximum K.E of the photoelectrons would be about

Moderate

A

$6.4 \times 10^{- 19} J$
B

$3.5 \times 10^{- 19} J$
C

$1.0 \times 10^{- 18} J$
D

$2.0 \times 10^{- 19} J$

Solution

$Given, λ = 200 nm = 200 \times 10^{- 9} m E = \frac{hC}{λ} = \frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{2 \times 10^{- 7}} = 9.9 \times 10^{- 19} J Work function, W = 6.4 \times 10^{- 19} J According to photoelectric effect, E = W + K . E K . E = 9.9 \times 10^{- 19} - 6.4 \times 10^{- 19} = 3.5 \times 10^{- 19} J$

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