JEE MAIN - Physics (2020 - 5th September Evening Slot)

1
An infinitely long, straight wire carrying current I, one side opened rectangular loop and a conductor C with a sliding connector are located in the same plane, as shown, in the figure. The connector has length $$l$$ and resistance R. It slides to the right with a velocity v. The resistance of the conductor and the self inductance of the loop are negligible. The induced current in the loop, as a function of separation r, between the connector and the straight wire is : JEE Main 2020 (Online) 5th September Evening Slot Physics - Electromagnetic Induction Question 81 English
Answer
(C)
$${{{\mu _0}} \over {2\pi }}{{Ivl} \over {Rr}}$$
2
In an experiment to verify Stokes law, a small spherical ball of radius r and density $$\rho $$ falls under gravity through a distance h in air before entering a tank of water. If the terminal velocity of the ball inside water is same as its velocity just before entering the water surface, then the value of h is proportional to :
(ignore viscosity of air)
Answer
(B)
r4
3
The velocity (v) and time (t) graph of a body in a straight line motion is shown in the figure. The point S is at 4.333 seconds. The total distance covered by the body in 6 s is : JEE Main 2020 (Online) 5th September Evening Slot Physics - Motion in a Straight Line Question 76 English
Answer
(D)
$${{37} \over 3}$$ m
4
Two coherent sources of sound, S1 and S2, produce sound waves of the same wavelength, $$\lambda $$ = 1 m, in phase. S1 and S2 are placed 1.5 m apart (see fig). A listener, located at L, directly in front of S2 finds that the intensity is at a minimum
when he is 2 m away from S2. The listener moves away from S1, keeping his distance from S2 fixed. The adjacent maximum of intensity is observed when the listener is at a distance d from S1. Then, d is : JEE Main 2020 (Online) 5th September Evening Slot Physics - Wave Optics Question 89 English
Answer
(C)
3 m
5
A galvanometer is used in laboratory for detecting the null point in electrical experiments. If, on passing a current of 6 mA it produces a deflection of 2o, its figure of merit is close to :
Answer
(C)
3 $$ \times $$ 10–3 A/div
6
A parallel plate capacitor has plate of length 'l', width ‘w’ and separation of plates is ‘d’. It is connected to a battery of emf V. A dielectric slab of the same thickness ‘d’ and of dielectric constant k = 4 is being inserted between the plates of the capacitor. At what length of the slab inside plates, will the energy stored in the capacitor be two times the initial energy stored?
Answer
(D)
$${l \over 3}$$
7
The acceleration due to gravity on the earth’s surface at the poles is g and angular velocity of the earth about the axis passing through the pole is $$\omega $$. An object is weighed at the equator and at a height h above the poles by using a spring balance. If the weights are found to be same, then h is (h << R, where R is the radius of the earth)
Answer
(A)
$${{{R^2}{\omega ^2}} \over {2g}}$$
8
In an adiabatic process, the density of a diatomic gas becomes 32 times its initial value. The final pressure of the gas is found to be n times the initial pressure. The value of n is :
Answer
(A)
128
9
An iron rod of volume 10–3 m3 and relative permeability 1000 is placed as core in a solenoid with 10 turns/cm. If a current of 0.5 A is passed through the solenoid, then the magnetic moment of the rod will be :
Answer
(A)
5 $$ \times $$ 102 Am2
10
In the circuit shown, charge on the 5 $$\mu $$F capacitor is :

JEE Main 2020 (Online) 5th September Evening Slot Physics - Capacitor Question 94 English
Answer
(D)
16.36 $$\mu $$C
11
In the circuit, given in the figure currents in different branches and value of one resistor are shown. Then potential at point B with respect to the point A is : JEE Main 2020 (Online) 5th September Evening Slot Physics - Current Electricity Question 212 English
Answer
(C)
+1 V
12
Two different wires having lengths L1 and L2, and respective temperature coefficient of linear expansion $$\alpha $$1 and $$\alpha $$2, are joined end-to-end. Then the effective temperature coefficient of linear expansion is :
Answer
(D)
$${{{\alpha _1}{L_1} + {\alpha _2}{L_2}} \over {{L_1} + {L_2}}}$$
13
Two Zener diodes (A and B) having breakdown voltages of 6 V and 4 V respectively, are connected as shown in the circuit below. The output voltage V0 variation with input voltage linearly increasing with time, is given by :
(Vinput = 0 V at t = 0)
(figures are qualitative) JEE Main 2020 (Online) 5th September Evening Slot Physics - Semiconductor Question 132 English
Answer
(D)
JEE Main 2020 (Online) 5th September Evening Slot Physics - Semiconductor Question 132 English Option 4
14
The correct match between the entries in column I and column II are :

I II
Radiation Wavelength
(a) Microwave (i) 100 m
(b) Gamma rays (ii) 10–15 m
(c) A.M. radio waves (iii) 10–10 m
(d) X-rays (iv) 10–3 m
Answer
(B)
(a)-(iv), (b)-(ii), (c)-(i), (d)-(iii)
15
Ten charges are placed on the circumference of a circle of radius R with constant angular separation between successive charges. Alternate charges 1, 3, 5, 7, 9 have charge (+q) each, while 2, 4, 6, 8, 10 have charge (–q) each. The potential V and the electric field E at the centre of the circle are respectively.
(Take V = 0 at infinity)
Answer
(A)
V = 0; E = 0
16
The quantities x = $${1 \over {\sqrt {{\mu _0}{\varepsilon _0}} }}$$, y = $${E \over B}$$ and z = $${l \over {CR}}$$ are
defined where C-capacitance, R-Resistance, l-length, E-Electric field, B-magnetic field and $${{\varepsilon _0}}$$, $${{\mu _0}}$$, - free space permittivity and permeability respectively. Then :
Answer
(B)
x, y and z have the same dimension
17
A spaceship in space sweeps stationary interplanetary dust. As a result, its mass
increases at a rate $${{dM\left( t \right)} \over {dt}}$$ = bv2(t), where v(t) is its instantaneous velocity. The instantaneous acceleration of the satellite is :
Answer
(C)
$$ - {{b{v^3}} \over {M\left( t \right)}}$$
18
A ring is hung on a nail. It can oscillate, without slipping or sliding
(i) in its plane with a time period T1 and,
(ii) back and forth in a direction perpendicular to its plane,
with a period T2. The ratio $${{{T_1}} \over {{T_2}}}$$ will be :
Answer
(B)
$${2 \over {\sqrt 3 }}$$
19
A body of mass 2 kg is driven by an engine delivering a constant power of 1 J/s. The body starts from rest and moves in a straight line. After 9 seconds, the body has moved a distance (in m) _______.
Answer
18
20
The surface of a metal is illuminated alternately with photons of energies E1 = 4 eV and E2 = 2.5 eV respectively. The ratio of maximum speeds of the photoelectrons emitted in the two cases is 2. The work function of the metal in (eV) is _____.
Answer
2
21
A prism of angle A = 1o has a refractive index $$\mu $$ = 1.5. A good estimate for the minimum angle of deviation (in degrees) is close to $${N \over {10}}$$.
Value of N is ____.
Answer
5
22
In the circuit shown, charge on the 5 $$\mu $$F capacitor is :

JEE Main 2020 (Online) 5th September Evening Slot Physics - Capacitor Question 94 English
Answer
(D)
16.36 $$\mu $$C
23
An infinitely long, straight wire carrying current I, one side opened rectangular loop and a conductor C with a sliding connector are located in the same plane, as shown, in the figure. The connector has length $$l$$ and resistance R. It slides to the right with a velocity v. The resistance of the conductor and the self inductance of the loop are negligible. The induced current in the loop, as a function of separation r, between the connector and the straight wire is : JEE Main 2020 (Online) 5th September Evening Slot Physics - Electromagnetic Induction Question 81 English
Answer
(C)
$${{{\mu _0}} \over {2\pi }}{{Ivl} \over {Rr}}$$