Question

# The radiation corresponding to 3→2 transition of hydrogen atom falls on a metal surface to produce photoelectrons. These electrons are made to enter a magnetic field of 3×10−4T. If the radius of the largest circular path followed by these electrons is 10.0 mm, the work function of the metal is close to

A
1.6 eV
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B
1.1 eV
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C
1.8 eV
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D
0.8 eV
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Solution

## The correct option is B 1.1 eVWhen an electron moves in a circular path, then evB=mv2r r=mveB r=√2meVeB or 1B√2mVeV=er2B22m→stopping potential V=100×10−6×1.6×10−19×9×10−82×9.1×10−31 =0.8 V KE of electron, K=0.8 eV For transition between 3 to 2, E=13.6(122−132) E=13.6×536E=1.88 eV Work fuction, ϕo=E−Kmax =1.89−0.79≈1.1 eV Hence, option B is correct.

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