The number of metals which will show photoelectric effect when light of wavelength 400 nm falls on it is ________ . [2023]

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Solution

Q.
Values of work function $(W_{0})$ for a few metals are given below:

Metal Li Na K Mg Cu Ag

$W_{0} / eV$ 2.42 2.3 2.25 3.7 4.8 4.3

The number of metals which will show photoelectric effect when light of wavelength 400 nm falls on it is ________ .

Given: $h = 6.6 \times 10^{- 34} J s$

$c = 3 \times 10^{8} {m s}^{- 1}$

$e = 1.6 \times 10^{- 19} C$ [2023]

Ans.
(3)

The energy of photon $(E) = \frac{h c}{λ}$

Given, $λ = 400$ $nm$

$E = \frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{400 \times 10^{- 9}}$

$E (in eV) = \frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{400 \times 10^{- 9} \times 1.6 \times 10^{- 19}} eV = 3.1 eV$

The metals Li, Na, K have a work function less than the energy of a photon. So in presence of light with wavelength 400 nm, they exhibit photoelectric effect.

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