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NEET 2011 (AIPMT, Prelims) · Photoelectric Effect: Einstein's Equation

Photoelectric Effect: Einstein's Equation question from NEET 2011 (AIPMT, Prelims)

Q156NEET 2011 · AIPMT · PRELIMSEasy

Photoelectric Effect: Einstein's Equation

Light of two different frequencies whose photons have energies 1 eV and 2.5 eV respectively illuminate a metallic surface whose work function is 0.5 eV successively. Ratio of maximum speeds of emitted electrons will be

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Answer: (b)

  1. 12mvmax2=E−ϕ\frac{1}{2}mv_{max}^2 = E - \phi, so vmax∝E−ϕv_{max} \propto \sqrt{E - \phi}.
  2. K1=1−0.5=0.5K_1 = 1 - 0.5 = 0.5 eV, K2=2.5−0.5=2K_2 = 2.5 - 0.5 = 2 eV
  3. v1v2=0.52=12\frac{v_1}{v_2} = \sqrt{\frac{0.5}{2}} = \frac{1}{2}
  4. So the answer is (b) 1:21:2.
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