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Question
The photoelectric work function for a metal is 4.2 eV. If the stopping potential is 3V, find the threshold wavelength and maximum kinetic energy of emitted electrons.
(Velocity of light in air = 3 x 108m/s,
Planck's constant = 6·63 x10-34 J -s,
Charg.e ori electron = 1·6 x 10 -19 C)
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Solution
`phi_0=(hc)/lambda_0`
`lambda_0=(hc)/phi_0`
`phi_0=4.2 e v=4.2 xx1.6xx10^(-19)J=6.72xx10^(-19)J`
`lambda_0=(hc)/phi_0=(6.63xx10^(-34)xx3xx10^8)/(6.72x10^(-19))`
`lambda_0=2.960xx10^(-7)m`
λ0 = 2960 A0
( K. E.)max = e Vs = 1.6 x 10-19 x 3
( K. E.)max = 4.8 x 10-19 J = 3 e V
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