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  4. The work function ( φ ) 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 φ( eV ) 2.4 2.3 2.2 3.7 4.8 4.3 4.7 6.3 4.75

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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

NTA AbhyasNTA Abhyas 2022

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.