JEE MAIN - Physics (2020 - 2nd September Evening Slot)
1
An inductance coil has a reactance of 100 $$\Omega $$.
When an AC signal of frequency 1000 Hz is
applied to the coil, the applied voltage leads
the current by 45o. The self-inductance of the
coil is
Answer
(D)
1.1 $$ \times $$ 10–2 H
2
In the following digital circuit, what will be the
output at ‘Z’, when the input (A, B) are (1, 0),
(0, 0), (1, 1,), (0, 1)
Answer
(D)
0, 0, 1, 0
3
A charge Q is distributed over two concentric
conducting thin spherical shells radii r and
R (R > r). If the surface charge densities on the
two shells are equal, the electric potential at
the common centre is :
Two uniform circular discs are rotating
independently in the same direction around
their common axis passing through their
centres. The moment of inertia and angular
velocity of the first disc are 0.1 kg-m2 and 10
rad s–1 respectively while those for the second
one are 0.2 kg-m2 and 5 rad s–1 respectively. At
some instant they get stuck together and start
rotating as a single system about their common
axis with some angular speed. The kinetic
energy of the combined system is :
Answer
(A)
$${{20} \over 3}J$$
5
A small point mass carrying some positive
charge on it, is released from the edge of a
table. There is a uniform electric field in this
region in the horizontal direction. Which of the
following options then correctly describe the
trajectory of the mass? (Curves are drawn
schematically and are not to scale).
Answer
(A)
6
The height ‘h’ at which the weight of a body will
be the same as that at the same depth ‘h’ from
the surface of the earth is (Radius of the earth
is R and effect of the rotation of the earth is
neglected)
Answer
(B)
$${{\sqrt 5 R - R} \over 2}$$
7
A particle is moving 5 times as fast as an
electron. The ratio of the de-Broglie wavelength
of the particle to that of the electron is 1.878 $$ \times $$
10–4. The mass of the particle is close to
Answer
(D)
9.7 $$ \times $$ 10–28 kg
8
A 10 $$\mu $$F capacitor is fully charged to a potential
difference of 50 V. After removing the source
voltage it is connected to an uncharged
capacitor in parallel. Now the potential
difference across them becomes 20 V. The
capacitance of the second capacitor is :
Answer
(B)
15 $$\mu $$F
9
A wire carrying current I is bent in the shape
ABCDEFA as shown, where rectangle ABCDA
and ADEFA are perpendicular to each other. If
the sides of the rectangles are of lengths a and
b, then the magnitude and direction of
magnetic moment of the loop ABCDEFA is
A capillary tube made of glass of radius 0.15
mm is dipped vertically in a beaker filled with
methylene iodide (surface tension = 0.05 Nm–1,
density = 667 kg m–3) which rises to height h in
the tube. It is observed that the two tangents
drawn from liquid-glass interfaces (from opp.
sides of the capillary) make an angle of 60o
with one another. Then h is close to (g = 10 ms–2)
Answer
(B)
0.087 m
11
The figure shows a region of length ‘l’ with a
uniform magnetic field of 0.3 T in it and a
proton entering the region with velocity 4 $$ \times $$ 105
ms–1 making an angle 60o with the field. If the
proton completes 10 revolution by the time it
cross the region shown, ‘l’ is close to (mass of
proton = 1.67 $$ \times $$ 10–27 kg, charge of the proton =
1.6 $$ \times $$ 10–19 C)
Answer
(D)
0.44 m
12
The displacement time graph of a particle
executing S.H.M is given in figure : (sketch is
schematic and not to scale)
Which of the following statements is/are true
for this motion?
(A) The force is zero at t = $${{3T} \over 4}$$
(B) The acceleration is maximum at t = T
(C) The speed is maximum at t = $${{T} \over 4}$$
(D) The P.E. is equal to K.E. of the oscillation at t = $${{T} \over 2}$$
Answer
(B)
(A), (B) and (C)
13
If momentum (P), area (A) and time (T) are
taken to be the fundamental quantities then the
dimensional formula for energy is
Answer
(C)
$$\left[ {P{A^{{1 \over 2}}}{T^{ - 1}}} \right]$$
14
In a hydrogen atom the electron makes a
transition from (n + 1)th level to the nth level.
If n >> 1, the frequency of radiation emitted is
proportional to :
Answer
(C)
$${1 \over {{n^3}}}$$
15
An ideal gas in a closed container is slowly
heated. As its temperature increases, which of
the following statements are true?
(A) the mean free path of the molecules
decreases.
(B) the mean collision time between the
molecules decreases.
(C) the mean free path remains unchanged.
(D) the mean collision time remains unchanged.
Answer
(C)
(B) and (C)
16
In a Young’s double slit experiment, 16 fringes
are observed in a certain segment of the
screen when light of a wavelength 700 nm is
used. If the wavelength of light is changed to
400 nm, the number of fringes observed in the
same segment of the screen would be
Answer
(A)
28
17
In a Young’s double slit experiment, 16 fringes
are observed in a certain segment of the
screen when light of a wavelength 700 nm is
used. If the wavelength of light is changed to
400 nm, the number of fringes observed in the
same segment of the screen would be
Answer
(A)
28
18
When the temperature of a metal wire is
increased from 0oC to 10oC, its length
increases by 0.02%. The percentage change in
its mass density will be closest to :
Answer
(B)
0.06
19
An ideal cell of emf 10 V is connected in circuit
shown in figure. Each resistance is 2 $$\Omega $$. The
potential difference (in V) across the capacitor
when it is fully charged is ______.
Answer
8
20
In a plane electromagnetic wave, the directions
of electric field and magnetic field are
represented by $$\widehat k$$ and $$2\widehat i - 2\widehat j$$, respectively.
What is the unit vector along direction of
propagation of the wave?
A square shaped hole of side l = $${a \over 2}$$ is carved
out at a distance d = $${a \over 2}$$ from the centre ‘O’ of
a uniform circular disk of radius a. If the
distance of the centre of mass of the
remaining portion form O is
$$ - {a \over X}$$ , value of X (to
the nearest integer) is :
Answer
23
22
A particle of mass m is moving along the x-axis
with initial velocity $$u\widehat i$$. It collides elastically
with a particle of mass 10 m at rest and then
moves with half its initial kinetic energy (see
figure). If $$\sin {\theta _1} = \sqrt n \sin {\theta _2}$$ then value of n is
________.
Answer
10
23
A light ray enters a solid glass sphere of
refractive index $$\mu $$ = $$\sqrt 3 $$ at an angle of incidence
60o. The ray is both reflected and refracted at
the farther surface of the sphere. The angle (in
degrees) between the reflected and refracted
rays at this surface is ________.