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. ($4.14$ ev)
Solution:
- Energy of photon
$ =\dfrac{h c}{\lambda} J=\dfrac{h c}{e \lambda} eV=\dfrac{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$.
BETA
