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BITSAT 2009
Exam
BITSAT
Year
2009
Subject
Physics
Chapter
Dual Nature of Matter

BITSAT 2009 · Physics · Dual Nature of Matter

In a photoelectric experiment, with light of wavelength λ, the...

In a photoelectric experiment, with light of wavelength λ,\lambda, the fastest electron has speed vv. If the exciting wavelength is changed to 3λ/43 \lambda / 4, the speed of the fastest emitted electron will become

Options

  1. Av34v \sqrt{\frac{3}{4}}
  2. Bv43v \sqrt{\frac{4}{3}}
  3. Cless than v43v \sqrt{\frac{4}{3}}
  4. Dgreater than v43v \sqrt{\frac{4}{3}}

Correct answer

D. greater than v43v \sqrt{\frac{4}{3}}

Step-by-step solution

12mv2=hcλ−ϕ\frac{1}{2} \mathrm{mv}^{2}=\frac{\mathrm{hc}}{\lambda}-\phi12m′=hc(3λ/4)−ϕ=4hc3λ−ϕ Clearly, v′>43v\begin{array}{l}\frac{1}{2} \mathrm{ m}^{\prime}=\frac{\mathrm{hc}}{(3 \lambda / 4)}-\phi=\frac{4 \mathrm{hc}}{3 \lambda}-\phi\\ \text{ Clearly, } \mathrm{v}^{\prime}>\sqrt{\frac{4}{3} \mathrm{v}} \end{array}$$
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