Q78 / 90 · JEE Main 2022 (24 Jun Shift 2) · Physics

The light of two different frequencies whose photons have energies 3.8eV and 1.4eV respectively, illuminate a metallic surface whose work function is 0.6eV successively. The ratio of maximum speeds of emitted electrons for the two frequencies respectively will be :

  • Correct answer
    A
    2:1
  • B
    4:1
  • C
    1:2
  • D
    1:4

Solution

Expression for maximum kinetic energy can be written as, KEmax=E-ϕ

KEmax, 1=E1-ϕ=3.8-0.6=3.2 eV, KEmax, 2=E2-ϕ=1.4-0.6=0.8 eV

KEmax, 1KEmax, 2=3.20.8=4⇒4=12 mv1212 mv22 

⇒v12v22=4 ⇒v1v2=2:1

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

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