Modern Physics 2 Question 8

8. The magnetic field associated with a light wave is given at the origin, by

B=B0[sin(3.14×107)ct+sin(6.28×107)ct].

If this light falls on a silver plate having a work function of 4.7eV, what will be the maximum kinetic energy of the photoelectrons?

(Main 2019, 10 Jan II) (Take, c=3×108ms1 and h=6.6×1034J-s)

(a) 7.72eV

(b) 6.82eV

(c) 8.52eV

(d) 12.5eV

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Solution:

  1. According to question, the wave equation of the magnetic field which produce photoelectric effect

B=B0[(sin(3.14×107ct)+sin(6.28×107ct)]

Here, the photoelectric effect produced by the angular frequency (ω)=6.28×107c

ω=6.28×107×3×108ω=2π×107×3×108rad/s

Using Eqs. (i)

hν=hω2π=h×2π×107×3×1082πhν=12.4eV

Therefore, according to Einstein equation for photoelectric effect

E=hν=φ+KEmaxKEmax=Eφ (where, φ= work-function =4.7eV ) KEmax=12.44.7=7.7eV or KEmax=7.7eV



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