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Question

The threshold frequency (V0) of Potassium metal is

A
5×1014Hz
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B
5.2×1010
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C
2×1012
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D
3.1×109Hz
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Solution

The correct option is A 5×1014Hz
Using eVs=hcλϕ
where ϕ is the work function of metal, hc=1241eV if wavelength is put in nm.
Case 1: λ=550nm,Vs=0.19V
0.19eV=1241550eVϕ
Or 0.19eV=2.256eVϕ
ϕ=2.07eV
Threshold frequency for the surface
vth=ϕh=2.07×1.6×10196.62×1034=5×1014Hz

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