Physics Circle home Student Login

Home›Chapters›Dual Nature of Radiation and Matter PYQs›Photoelectric Effect: Einstein's Equation›Question 117

JEE Main 2021 (25 Jul, Shift 2) · Photoelectric Effect: Einstein's Equation

Photoelectric Effect: Einstein's Equation question from JEE Main 2021 (25 Jul, Shift 2)

Q117JEE Main 2021 · 25 JUL · SHIFT 2Difficult

Photoelectric Effect: Einstein's Equation

A light beam of wavelength 500 nm is incident on a metal having work function of 1.25 eV, placed in a magnetic field of intensity B. The electrons emitted perpendicular to the magnetic field B, with maximum kinetic energy are bent into circular arc of radius 30 cm. The value of B is ___________ ×\times 10−-7 T.

Given hc = 20 ×\times 10−-26 J-m, mass of electron = 9 ×\times 10 −-31 kg

Numerical answer type. Work it out, then open the answer.

Show answer and solution

Answer: 125

  1. E=hcλ=20×10−26500×10−9=4×10−19E = \frac{hc}{\lambda} = \frac{20 \times 10^{-26}}{500 \times 10^{-9}} = 4 \times 10^{-19} J =2.5= 2.5 eV.
  2. K=2.5−1.25=1.25K = 2.5 - 1.25 = 1.25 eV =2×10−19= 2 \times 10^{-19} J
  3. p=2mK=2×9×10−31×2×10−19=6×10−25p = \sqrt{2mK} = \sqrt{2 \times 9 \times 10^{-31} \times 2 \times 10^{-19}} = 6 \times 10^{-25} kg m/s
  4. B=per=6×10−251.6×10−19×0.3=1.25×10−5B = \frac{p}{er} = \frac{6 \times 10^{-25}}{1.6 \times 10^{-19} \times 0.3} = 1.25 \times 10^{-5} T =125×10−7= 125 \times 10^{-7} T
  5. So the answer is 125.
Report a mistake

More questions on Photoelectric Effect: Einstein's Equation