Q67 / 90 · JEE Main 2016 (03 Apr) · Physics

Radiation of wavelength λ is incident on a photocell. The fastest emitted photoelectron has a speed v. If the wavelength is changed to 3λ4, the speed of the fastest emitted photoelectron will be

  • A
    =v4312
  • B
    =v3412
  • Correct answer
    C
    >v4312
  • D
    <v4312

Solution

12mv2=hcλ-ϕ ...(i)

12mv'2=43hcλ-ϕ  ...(ii)

From Eqn. (i)

hcλ=12mv2+ϕ

On putting this Equation (ii)

12mv′2=4312mv2+ϕ-ϕ

v'2=43v2+2ϕ3m

⇒v'>43v

Hence, the correct answer is option: 'C'.

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