Two particles move at right angle to each… - JEE Main 2019 Physics PYQ

JEE Main 2019 — Physics Modern Physics

2019mcqmedium

Two particles move at right angle to each other. Their de Broglie wavelengths are ${\lambda }_{1}$ and ${\lambda }_{2}$ respectively. The particles suffer perfectly inelastic collision. The de Broglie wavelength $\lambda$ of the final particle, is given by:

Official previous-year question

Held on 8 Apr 2019 · Verified 6 Jul 2026.

Options

A
$\frac{2}{\lambda }=\frac{1}{{\lambda }_{1}}+\frac{1}{{\lambda }_{2}}$
B
$\lambda =\frac{{\lambda }_{1}+{\lambda }_{2}}{2}$
C
$\lambda =\sqrt{{\lambda }_{1}{\lambda }_{2}}$
D
$\frac{1}{{\lambda }^{2}}=\frac{1}{{\lambda }_{1}^{2}}+\frac{1}{{\lambda }_{2}^{2}}$

Did you get this right?

Solution

$\vec{{P}_{1}}=\frac{h}{{\lambda }_{1}}\hat{i}\text{,} \vec{{P}_{2}}=\frac{h}{{\lambda }_{2}}\hat{j}$

$\vec{P}=\vec{{P}_{1}}+\vec{{P}_{2}}=\frac{h}{{\lambda }_{1}}\hat{i}+\frac{h}{{\lambda }_{2}}\hat{j}$

$|\vec{P}|=h\sqrt{\frac{1}{{\lambda }_{1}^{2}}+\frac{1}{{\lambda }_{2}^{2}}}$

$\frac{h}{\lambda }=h\sqrt{\frac{1}{{\lambda }_{1}^{2}}+\frac{1}{{\lambda }_{2}^{2}}}$

$\frac{1}{{\lambda }^{2}}=\frac{1}{{\lambda }_{1}^{2}}+\frac{1}{{\lambda }_{2}^{2}}$

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 2018 Modern Physics 2017 Modern Physics 2016 Modern Physics 2015 Modern Physics 2014

More JEE Main Modern Physics questions

An electron of mass $m$ is moving in an electric field $\vec{E} = -2E_0\hat{i}$ ($E_0 =$ constant $> 0$), with an initial velocity $\vec{V} = v_0\hat{i}$ ($v_0 =$ constant $> 0$). If $\lambda_0 = \dfrac{h}{4mv_0}$, its de Broglie wavelength at time $t$ is __________. ($e =$ charge of electron)

2026medium

In a semiconductor p-n diode, the doping concentrations on p-side and n-side are $10^{15}\text{ atoms/cm}^3$ and $10^{18}\text{ atoms/cm}^3$, respectively. Which one of the following statements is true ?

2026easy

The following diagram shows a Zener diode as a voltage regulator. The Zener diode is rated at $V_{z}=5 \mathrm{~V}$ and the desired current in load is 5 mA. The unregulated voltage source can supply upto 25 V. Considering the Zener diode can withstand four times of the load current, the value of resistor $R_{S}$ (shown in circuit) should be $\_\_\_\_$ $\Omega$. ![JEE Main 2026 Physics, Semiconductors — question figure](https://prepforbharat.s3.ap-south-1.amazonaws.com/exam/615f0e999476412f48314daf/Physics/images/Semiconductors/698a0b35c573c2d03372efcc/question_1__q_698a0b35c573c2d03372efcc__cdn-question-pool.getmarks.app__23S1_q_30_1__216b0f1417_final_ppt_sync.png)

2026medium

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): The electromagnetic wave exerts pressure on the surface on which they are allowed to fall. Reason (R): There is no mass associated with the electromagnetic waves. In the light of the above statements, choose the correct answer from the options given below :

2026medium

In hydrogen atom spectrum, $(R \rightarrow$ Rydberg's constant $)$ A. the maximum wavelength of the radiation of Lyman series is $\frac{4}{3 R}$ B. the Balmer series lies in the visible region of the spectrum C. the minimum wavelength of the radiation of Paschen series is $\frac{9}{R}$ D. the minimum wavelength of Lyman series is $\frac{5}{4 R}$ Choose the correct answer from the options given below :

2026medium

View all Modern Physics questions

Keep practicing Modern Physics

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

Browse all Physics topics

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