Q149 / 200 · NEET 2022 (Phase 1) · Physics

When two monochromatic lights of frequency, ν and ν2 are incident on a photoelectric metal, their stopping potential becomes VS2 and Vs respectively. The threshold frequency for this metal is:

  • A
    3ν
  • B
    23ν
  • Correct answer
    C
    32ν
  • D
    2ν

Solution

Using Einstein's photoelectric equation we can write,

For first case:

hν=ϕ+eVS2   ...1

For second case:

hν2=ϕ+eVS   ...2

Using value of eVS from equation(2) in equation(1), we can write,

hν=ϕ+12hν2-ϕ
⇒hν=ϕ+hν4-ϕ2
⇒ϕ2=3hν4
⇒ϕ=3hν2

As we know, ϕ=hν0

Therefore, ν0=3ν2

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

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