Q.
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 metals is :
Metakl
Li
N
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
Metakl | Li | N | 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 |
Solution:
Energy of photon $=\frac{\text{h} \text{c}}{\lambda }\text{J}=\frac{\text{h} \text{c}}{\text{e} \lambda }\text{e}\text{V}$
$=\frac{6.625 \times 10^{- 34} \times 3 \times 10^{8}}{300 \times 10^{- 9} \times 1.602 \times 10^{- 19}}=4.14 \, \text{e}\text{V}$
For photoelectric effect to occur, energy of incident photons, must be greater than work functions of metal. Hence, only Li, Na, K and Mg have work functions less than 4.14 eV.
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