JEE Main 2020 Question Paper (09-Jan-2020) (Shift 2)

Question 1

The current $i$ in the network is

Accepted Answer

$0.3\mathrm{A}$

Answer

$0.2 \mathrm{A}$

Answer

$0.6 \mathrm{A}$

Answer

$0 \mathrm{A}$

Question 2

A wire of length $L$ and mass per unit length $6.0 	imes 10^{-3} \ \mathrm{kg \ m^{-1}}$ is put under a tension of $540 \ \mathrm{N}$. Two consecutive frequencies at which it resonates are $420 \ \mathrm{Hz}$ and $490 \ \mathrm{Hz}$. Then $L$ in meters is:

Accepted Answer

$2.1\,\mathrm{m}$

Answer

$1.1\,\mathrm{m}$

Answer

$8.1\,\mathrm{m}$

Answer

$5.1\,\mathrm{m}$

Question 3

An electron of mass $m$ and magnitude of charge $e$ at rest gets accelerated by a constant electric field $E$. The rate of change of the de-Broglie wavelength of this electron at a time $t$ is (ignore relativistic effects):

Accepted Answer

$ \frac{d\lambda}{dt} = -\frac{h}{eE t^{2}} $

Answer

$ \frac{d\lambda}{dt} = -\frac{h}{e E t} $

Answer

$ \frac{d\lambda}{dt} = -\frac{2h}{eEt} $

Answer

$ \frac{d\lambda}{dt} = -\frac{2h}{eE t^{2}} $

Question 4

In an $LC$ circuit, the inductance $L = 40 \mathrm{mH}$ and capacitance $C = 100 \mathrm{\mu F}$. If a voltage $V(t) = 10 \sin(314t)$ is applied to the circuit, the current in the circuit is given as:

Accepted Answer

$0.52 \cos(314t)$

Answer

$10 \cos\left(314 t\right)$

Answer

$5.2 \cos\left(314 t\right)$

Answer

$0.52 \sin(314t)$

Question 5

A small circular loop of conducting wire has radius $ a $ and carries current $ I $. It is placed in a uniform magnetic field $ B $ perpendicular to its plane such that when rotated slightly about its diameter and released, it starts performing simple harmonic motion of time period $ T $. The mass of the loop is $ m $, then:

Accepted Answer

$ T = \sqrt{\frac{2\pi m}{iB}}$

Answer

$ T = \sqrt{\frac{2m}{iB}} $

Answer

$ T = \sqrt{\frac{\pi m}{2 i B}}$

Answer

$ T = \sqrt{\frac{\pi m}{i B}} $