Atomic Structure - Result Question 94

####70. The work function $(\phi)$ of some metals is listed below. The number of metals which will show photoelectric effect when light of $300 nm$ wavelength falls on the metal is

(2011)

Metal $Li$ $Na$ $K$ $Mg$ $Cu$ $Ag$ $Fe$ $Pt$ $W$
$\Phi(eV)$ 2.4 2.3 2.2 3.7 4.8 4.3 4.7 6.3 4.75
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Answer:

Correct Answer: 70. (9)

Solution:

  1. Energy of photon

$$ =\frac{h c}{\lambda} J=\frac{h c}{e \lambda} eV=\frac{6.625 \times 10^{-34} \times 3 \times 10^{8}}{300 \times 10^{-9} \times 1.602 \times 10^{-19}}=4.14 eV $$

For photoelectric effect to occur, energy of incident photons must be greater than work function of metal. Hence, only Li, Na, $K$ and $Mg$ have work functions less than $4.14 V$.



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