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Question

The electric field associated with a light wave is E=E0sin(1.57 ×107(xct)), where x is in meter and t is in second. If this light is used to produce photoelectric emission, from the surface of a metal has a work function 1.9 eV, then the stopping potential will be ?

A
1.2 V
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B
1.5 V
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C
1.75 V
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D
1.9 V
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Solution

The correct option is A 1.2 V
Comparing the the given expression for electric filed with the standard expression, E=E0sin(kxωt)
we get k=1.57×107m1 where k is propagation constant which is related to wavelength, λ as
follows k=2πλ so putting value of k we get λ=4×107m=4000Angstrom
So energy of incident photon will be E=hcλ=124004000ev=3.1eV
Out of which 1.9eV will be consumed against work function,W=1.9eV so maximum kinetic energy KEmax=3.1eV1.9eV=1.2eV
So the stopping potential will be V0=KEmaxcharge=1.2eVe=1.2V

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