JEE MAIN - Physics (2021 - 27th July Evening Shift)

1
An electron and proton are separated by a large distance. The electron starts approaching the proton with energy 3 eV. The proton captures the electron and forms a hydrogen atom in second excited state. The resulting photon is incident on a photosensitive metal of threshold wavelength 4000$$\mathop A\limits^o $$. What is the maximum kinetic energy of the emitted photoelectron?
Answer
(B)
1.41 eV
2
The expected graphical representation of the variation of angle of deviation '$$\delta$$' with angle of incidence 'i' in a prism is :
Answer
(B)
JEE Main 2021 (Online) 27th July Evening Shift Physics - Geometrical Optics Question 115 English Option 2
3
A raindrop with radius R = 0.2 mm falls from a cloud at a height h = 2000 m above the ground. Assume that the drop is spherical throughout its fall and the force of buoyance may be neglected, then the terminal speed attained by the raindrop is :

[Density of water fw = 1000 kg m$$-$$3 and Density of air fa = 1.2 kg m$$-$$3, g = 10 m/s2, Coefficient of viscosity of air = 1.8 $$\times$$ 10$$-$$5 Nsm$$-$$2]
Answer
(C)
4.94 ms$$-$$1
4
One mole of an ideal gas is taken through an adiabatic process where the temperature rises from 27$$^\circ$$ C to 37$$^\circ$$ C. If the ideal gas is composed of polyatomic molecule that has 4 vibrational modes, which of the following is true? [R = 8.314 J mol$$-$$1 k$$-$$1]
Answer
(B)
work done on the gas is close to 582 J
5
An object of mass 0.5 kg is executing simple harmonic motion. It amplitude is 5 cm and time period (T) is 0.2 s. What will be the potential energy of the object at an instant $$t = {T \over 4}s$$ starting from mean position. Assume that the initial phase of the oscillation is zero.
Answer
(A)
0.62 J
6
Match List I with List II.

List - I List - II
(a) Capacitance, C (i) $${M^1}{L^1}{T^{ - 3}}{A^{ - 1}}$$
(b) Permittivity of free space, $${\varepsilon _0}$$ (ii) $${M^{ - 1}}{L^{ - 3}}{T^4}{A^2}$$
(c) Permeability of free space, $${\mu _0}$$ (iii) $${M^{ - 1}}{L^{ - 2}}{T^4}{A^2}$$
(d) Electric field, E (iv) $${M^1}{L^1}{T^{ - 2}}{A^{ - 2}}$$


Choose the correct answer from the options given below
Answer
(A)
(a) $$\to$$ (iii), (b) $$\to$$ (ii), (c) $$\to$$ (iv), (d) $$\to$$ (i)
7
Given below is the plot of a potential energy function U(x) for a system, in which a particle is in one dimensional motion, while a conservative force F(x) acts on it. Suppose that Emech = 8 J, the incorrect statement for this system is :

JEE Main 2021 (Online) 27th July Evening Shift Physics - Work Power & Energy Question 75 English
[ where K.E. = kinetic energy ]
Answer
(B)
at x < x1, K.E. is smallest and the particle is moving at the slowest speed.
8
A 100$$\Omega$$ resistance, a 0.1 $$\mu$$F capacitor and an inductor are connected in series across a 250 V supply at variable frequency. Calculate the value of inductance of inductor at which resonance will occur. Given that the resonant frequency is 60 Hz.
Answer
(D)
70.3 H
9
A simple pendulum of mass 'm', length 'l' and charge '+ q' suspended in the electric field produced by two conducting parallel plates as shown. The value of deflection of pendulum in equilibrium position will be

JEE Main 2021 (Online) 27th July Evening Shift Physics - Capacitor Question 77 English
Answer
(C)
$${\tan ^{ - 1}}\left[ {{q \over {mg}} \times {{{C_2}({V_1} + {V_2})} \over {({C_1} + {C_2})(d - t)}}} \right]$$
10
Find the truth table for the function Y of A and B represented in the following figure.

JEE Main 2021 (Online) 27th July Evening Shift Physics - Semiconductor Question 101 English
Answer
(B)
JEE Main 2021 (Online) 27th July Evening Shift Physics - Semiconductor Question 101 English Option 2
11
Figure A and B shown to long straight wires of circular cross-section (a and b with a < b), carrying current I which is uniformly distributed across the cross-section. The magnitude of magnetic field B varies with radius r and can be represented as :

JEE Main 2021 (Online) 27th July Evening Shift Physics - Magnetic Effect of Current Question 113 English
Answer
(C)
JEE Main 2021 (Online) 27th July Evening Shift Physics - Magnetic Effect of Current Question 113 English Option 3
12
Two identical particles of mass 1 kg each go round a circle of radius R, under the action of their mutual gravitational attraction. The angular speed of each particle is :
Answer
(B)
$${1 \over 2}\sqrt {{G \over {{R^3}}}} $$
13
What will be the magnitude of electric field at point O as shown in the figure? Each side of the figure is l and perpendicular to each other?

JEE Main 2021 (Online) 27th July Evening Shift Physics - Electrostatics Question 120 English
Answer
(B)
$${1 \over {4\pi {\varepsilon _0}}}{q \over {(2{l^2})}}\left( {2\sqrt 2 - 1} \right)$$
14
A physical quantity 'y' is represented by the formula $$y = {m^2}{r^{ - 4}}{g^x}{l^{ - {3 \over 2}}}$$

If the percentage errors found in y, m, r, l and g are 18, 1, 0.5, 4 and p respectively, then find the value of x and p.
Answer
(C)
$${{16} \over 3}$$ and $$ \pm {3 \over 2}$$
15
An automobile of mass 'm' accelerates starting from origin and initially at rest, while the engine supplies constant power P. The position is given as a function of time by :
Answer
(D)
$${\left( {{{8P} \over {9m}}} \right)^{{1 \over 2}}}{t^{{3 \over 2}}}$$
16
The planet Mars has two moons, if one of them has a period 7 hours, 30 minutes and an orbital radius of 9.0 $$\times$$ 103 km. Find the mass of Mars.

$$\left\{ {Given\,{{4{\pi ^2}} \over G} = 6 \times {{10}^{11}}{N^{ - 1}}{m^{ - 2}}k{g^2}} \right\}$$
Answer
(D)
6.00 $$\times$$ 1023 kg
17
A particle of mass M originally at rest is subjected to a force whose direction is constant but magnitude varies with time according to the relation

$$F = {F_0}\left[ {1 - {{\left( {{{t - T} \over T}} \right)}^2}} \right]$$

Where F0 and T are constants. The force acts only for the time interval 2T. The velocity v of the particle after time 2T is :
Answer
(C)
4F0T/3M
18
The resistance of a conductor at 15$$^\circ$$C is 16$$\Omega$$ and at 100$$^\circ$$C is 20$$\Omega$$. What will be the temperature coefficient of resistance of the conductor?
Answer
(C)
0.003$$^\circ$$C$$-$$1
19
In the given figure, two wheels P and Q are connected by a belt B. The radius of P is three times as that of Q. In case of same rotational kinetic energy, the ratio of rotational inertias $$\left( {{{{I_1}} \over {{I_2}}}} \right)$$ will be x : 1. The value of x will be _____________.
JEE Main 2021 (Online) 27th July Evening Shift Physics - Rotational Motion Question 88 English
Answer
9
20
The difference in the number of waves when yellow light propagates through air and vacuum columns of the same thickness is one. The thickness of the air column is ___________ mm. [Refractive index of air = 1.0003, wavelength of yellow light in vacuum = 6000 $$\mathop A\limits^o $$]
Answer
2
21
In the given figure the magnetic flux through the loop increases according to the relation $$\phi$$B(t) = 10t2 + 20t, where $$\phi$$B is in milliwebers and t is in seconds.

The magnitude of current through R = 2$$\Omega$$ resistor at t = 5 s is ___________ mA.

JEE Main 2021 (Online) 27th July Evening Shift Physics - Electromagnetic Induction Question 71 English
Answer
60
22
A particle executes simple harmonic motion represented by displacement function as

x(t) = A sin($$\omega$$t + $$\phi$$)

If the position and velocity of the particle at t = 0 s are 2 cm and 2$$\omega$$ cm s$$-$$1 respectively, then its amplitude is $$x\sqrt 2 $$ cm where the value of x is _________________.
Answer
2
23
A swimmer wants to cross a river from point A to point B. Line AB makes an angle of 30$$^\circ$$ with the flow of river. Magnitude of velocity of the swimmer is same as that of the river. The angle $$\theta$$ with the line AB should be _________$$^\circ$$, so that the swimmer reaches point B.

JEE Main 2021 (Online) 27th July Evening Shift Physics - Motion in a Plane Question 48 English
Answer
30
24
For the circuit shown, the value of current at time t = 3.2 s will be _________ A.


[Voltage distribution V(t) is shown by Fig. (1) and the circuit is shown in Fig. (2)]
Answer
1
25
A small block slides down from the top of hemisphere of radius R = 3 m as shown in the figure. The height 'h' at which the block will lose contact with the surface of the sphere is __________ m.

(Assume there is no friction between the block and the hemisphere)

JEE Main 2021 (Online) 27th July Evening Shift Physics - Work Power & Energy Question 76 English
Answer
2
26
The K$$\alpha$$ X-ray of molybdenum has wavelength 0.071 nm. If the energy of a molybdenum atoms with a K electron knocked out is 27.5 keV, the energy of this atom when an L electron is knocked out will be __________ keV. (Round off to the nearest integer)

[h = 4.14 $$\times$$ 10$$-$$15 eVs, c = 3 $$\times$$ 108 ms$$-$$1]
Answer
10
27
The water is filled upto height of 12 m in a tank having vertical sidewalls. A hole is made in one of the walls at a depth 'h' below the water level. The value of 'h' for which the emerging steam of water strikes the ground at the maximum range is ________ m.
Answer
6