JEE Main 2016 — Physics Modern Physics

2016mcqmedium

Radiation of wavelength $\lambda$ is incident on a photocell. The fastest emitted photoelectron has a speed $v$ . If the wavelength is changed to $\frac{3\lambda }{4}$ , the speed of the fastest emitted photoelectron will be

Official previous-year question

Held on 3 Apr 2016 · Verified 6 Jul 2026.

Options

A
$=v{(\frac{4}{3})}^{\frac{1}{2}}$
B
$=v{(\frac{3}{4})}^{\frac{1}{2}}$
C
$>v{(\frac{4}{3})}^{\frac{1}{2}}$
D
$<v{(\frac{4}{3})}^{\frac{1}{2}}$

Did you get this right?

Solution

$\frac{1}{2}{\mathrm{mv}}^{2}=\frac{\mathrm{hc}}{\lambda }-\phi$ ...(i)

$\frac{1}{2}\mathrm{mv}{'}^{2}=\frac{4}{3}\frac{\mathrm{hc}}{\lambda }-\phi$ ...(ii)

From Eqn. (i)

$\frac{\mathrm{hc}}{\lambda }=\frac{1}{2}{\mathrm{mv}}^{2}+\phi$

On putting this Equation (ii)

$\frac{1}{2}{\mathrm{mv}}^{'2}=\frac{4}{3}(\frac{1}{2}{\mathrm{mv}}^{2}+\phi )-\phi$

$v{'}^{2}=\frac{4}{3}{v}^{2}+\frac{2\phi }{3m}$

$\Rightarrow v'>\sqrt{\frac{4}{3}}v$

Your note

JEE Main Modern Physics in other years

Modern Physics 2026 Modern Physics 2025 Modern Physics 2024 Modern Physics 2023 Modern Physics 2022 Modern Physics 2021 Modern Physics 2020 Modern Physics 2019 Modern Physics 2018 Modern Physics 2017 Modern Physics 2015 Modern Physics 2014

Keep practicing Modern Physics

Work through every JEE Main Modern Physics PYQ, year by year.

Browse all Physics topics

Solution

$\frac{1}{2}{\mathrm{mv}}^{2}=\frac{\mathrm{hc}}{\lambda }-\phi$ ...(i)

$\frac{1}{2}\mathrm{mv}{'}^{2}=\frac{4}{3}\frac{\mathrm{hc}}{\lambda }-\phi$ ...(ii)

From Eqn. (i)

$\frac{\mathrm{hc}}{\lambda }=\frac{1}{2}{\mathrm{mv}}^{2}+\phi$

On putting this Equation (ii)

$\frac{1}{2}{\mathrm{mv}}^{'2}=\frac{4}{3}(\frac{1}{2}{\mathrm{mv}}^{2}+\phi )-\phi$

$v{'}^{2}=\frac{4}{3}{v}^{2}+\frac{2\phi }{3m}$

$\Rightarrow v'>\sqrt{\frac{4}{3}}v$

JEE Main 2016 — Physics Modern Physics

Options

Did you get this right?

Solution

Your note

JEE Main Modern Physics in other years

More JEE Main Modern Physics questions

Other Physics topics for JEE Main

Mechanics

Electromagnetism

Optics

Thermodynamics

Waves & Oscillations

Keep practicing Modern Physics

JEE Main 2016 — Physics Modern Physics

Options

Did you get this right?

Solution

Your note

JEE Main Modern Physics in other years

More JEE Main Modern Physics questions

Other Physics topics for JEE Main

Mechanics

Electromagnetism

Optics

Thermodynamics

Waves & Oscillations

Keep practicing Modern Physics