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BITSAT 2018
Exam
BITSAT
Year
2018
Subject
Physics
Chapter
Dual Nature of Matter

BITSAT 2018 · Physics · Dual Nature of Matter

The frequency and the intensity of incident beam of light falling...

The frequency and the intensity of incident beam of light falling on the surface of a photoelectric material is increased by a factor of two. This will

Options

  1. Aincrease the maximum kinetic energy of the ejected photoelectrons by a factor of more than two and would increase the photoelectric current by a factor of two.
  2. Bincrease the maximum kinetic energy of the photo electron& and would increase the photoelectric current both by a factor of two.
  3. Cincrease the maximum kinetic energy of the photoelectron by a factor of two and will have no effect on the magnitude of the photoelectric current produced.
  4. Dnot produce any effect on the kinetic energy of the emitted photoelectrons but will increase the photoelectric current by a factor of two.

Correct answer

A. increase the maximum kinetic energy of the ejected photoelectrons by a factor of more than two and would increase the photoelectric current by a factor of two.

Step-by-step solution

Using Einstein's photoelectric equations,

hv=ϕ+eVshv = ϕ + e{V}_{s}

eVs=hv−ϕ....(i)e{V}_{s} = hv - ϕ.... ( i )

Thus, when the frequency of incident light radiation (photons) vv increases to 2v2v, the stopping potential Vs{V}_{s} changes to Vs{V}_{s}

eVs′=h(2v)−ϕ....(ii)e{V}_s^{'} = h ( 2v ) - ϕ.... \left(ii\right)

On dividing Eq. (ii) by Eq. (ii), we get

Vs′Vs=2hv−ϕhv−ϕ=2hv−2ϕ+ϕhv−ϕ\dfrac{{V}_{s} '}{Vs} = \dfrac{2hv - ϕ}{hv - ϕ} = \dfrac{2hv - 2ϕ + ϕ}{hv - ϕ}

=2(hv−ϕ)+ϕhv−ϕ=2+ϕhv−ϕ= \dfrac{2 ( hv - ϕ ) + ϕ}{hv - ϕ} =2 + \dfrac{ϕ}{hv - ϕ}

∴V′sVs∴ \dfrac{V^{'}s}{Vs}> 2 ⇒ {V}_s^{'} > 2{V}_{s}</p></p>

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