JEE MAIN - Physics (2021 - 18th March Morning Shift)

1
An oil drop of radius 2 mm with a density 3g cm^$$-$$3 is held stationary under a constant electric field 3.55 $$\times$$ 10⁵ V m^$$-$$1 in the Millikan's oil drop experiment. What is the number of excess electrons that the oil drop will possess? (consider g = 9.81 m/s²)
პასუხი
(B)
1.73 $$\times$$ 10¹⁰
2
Imagine that the electron in a hydrogen atom is replaced by a muon ($$\mu$$). The mass of muon particle is 207 times that of an electron and charge is equal to the charge of an electron. The ionization potential of this hydrogen atom will be :
პასუხი
(B)
2815.2 eV
3
A plane electromagnetic wave of frequency 100 MHz is travelling in vacuum along the x-direction. At a particular point in space and time, $$\overrightarrow B = 2.0 \times {10^{ - 8}}\widehat kT$$. (where, $$\widehat k$$ is unit vector along z-direction) What is $$\overrightarrow E $$ at this point?
პასუხი
(C)
6.0 $$\widehat j$$ V/m
4
A thin circular ring of mass M and radius r is rotating about its axis with an angular speed $$\omega$$. Two particles having mass m each are now attached at diametrically opposite points. The angular speed of the ring will become :
პასუხი
(C)
$$\omega {M \over {M + 2m}}$$
5
Four identical long solenoids A, B, C and D are connected to each other as shown in the figure. If the magnetic field at the center of A is 3T, the field at the center of C would be : (Assume that the magnetic field is confined with in the volume of respective solenoid).

პასუხი
(D)
1T
6
The P-V diagram of a diatomic ideal gas system going under cyclic process as shown in figure. The work done during an adiabatic process CD is (use $$\gamma$$ = 1.4) :

პასუხი
(A)
$$-$$500 J
7
In Young's double slit arrangement, slits are separated by a gap of 0.5 mm, and the screen is placed at a distance of 0.5 m from them. The distance between the first and the third bright fringe formed when the slits are illuminated by a monochromatic light of 5890 $$\mathop A\limits^o $$ is :-
პასუხი
(B)
1178 $$\times$$ 10^$$-$$6 m
8
A particle is travelling 4 time as fast as an electron. Assuming the ratio of de-Broglie wavelength of a particle to that of electron is 2 : 1, the mass of the particle is :
პასუხი
(D)
$${1 \over {8}}$$ times the mass of e^$$-$$
9
The position, velocity and acceleration of a particle moving with a constant acceleration can be represented by :
პასუხი
(B)
10
In the experiment of Ohm's law, a potential difference of 5.0 V is applied across the end of a conductor of length 10.0 cm and diameter of 5.00 mm. The measured current in the conductor is 2.00 A. The maximum permissible percentage error in the resistivity of the conductor is :
პასუხი
(A)
3.9
11
In a series LCR resonance circuit, if we change the resistance only, from a lower to higher value :
პასუხი
(A)
The bandwidth of resonance circuit will increase.
12
An AC source rated 220 V, 50 Hz is connected to a resistor. The time taken by the current to change from its maximum to the rms value is :
პასუხი
(A)
2.5 ms
13
Your friend is having eye sight problem. She is not able to see clearly a distant uniform window mesh and it appears to her as non-uniform and distorted. The doctor diagnosed the problem as :
პასუხი
(B)
Myopia with Astigmatism
14
A loop of flexible wire of irregular shape carrying current is placed in an external magnetic field. Identify the effect of the field on the wire.
პასუხი
(A)
Loop assumes circular shape with its plane normal to the field.
15
The time period of a satellite in a circular orbit of radius R is T. The period of another satellite in a circular orbit of radius 9R is :
პასუხი
(B)
27 T
16
A particle performs simple harmonic motion with a period of 2 second. The time taken by the particle to cover a displacement equal to half of its amplitude from the mean position is $${1 \over a}$$s. The value of 'a' to the nearest integer is _________.
პასუხი
6
17
The circuit shown in the figure consists of a charged capacitor of capacity 3 $$\mu$$F and a charge of $$\mu$$C. At time t = 0, when the key is closed, the value of current flowing through the 5 M$$\Omega$$ resistor is 'x' $$\mu$$-A. The value of 'x to the nearest integer is ___________.

პასუხი
2
18
The voltage across the 10$$\Omega$$ resistor in the given circuit is x volt.

The value of 'x' to the nearest integer is _________.
პასუხი
70
19
Two separate wires A and B are stretched by 2 mm and 4 mm respectively, when they are subjected to a force of 2 N. Assume that both the wires are made up of same material and the radius of wire B is 4 times that of the radius of wire A. The length of the wires A and B are in the ratio of a : b. Then a/b can be expressed as 1/x where x is _________.
პასუხი
32
20
A person is swimming with a speed of 10 m/s at an angle of 120$$^\circ$$ with the flow and reaches to a point directly opposite on the other side of the river. The speed of the flow is 'x' m/s. The value of 'x' to the nearest integer is __________.
პასუხი
5
21
A parallel plate capacitor has plate area 100 m² and plate separation of 10 m. The space between the plates is filled up to a thickness 5 m with a material of dielectric constant of 10. The resultant capacitance of the system is 'x' pF.

The value of $$\varepsilon $$₀ = 8.85 $$\times$$ 10^$$-$$12 F.m^$$-$$1.

The value of 'x' to the nearest integer is _____________.
პასუხი
161
22
A ball of mass 10 kg moving with a velocity 10$$\sqrt 3 $$ m/s along the x-axis, hits another ball of mass 20 kg which is at rest. After the collision, first ball comes to rest while the second ball disintegrates into two equal pieces. One piece starts moving along y-axis with a speed of 10 m/s. The second piece starts moving at an angle of 30$$^\circ$$ with respect to the x-axis. The velocity of the ball moving at 30$$^\circ$$ with x-axis is x m/s. The configuration of pieces after collision is shown in the figure below. The value of x to the nearest integer is ____________.

პასუხი
20
23
As shown in the figure, a particle of mass 10 kg is placed at a point A. When the particle is slightly displaced to its right, it starts moving and reaches the point B. The speed of the particle at B is x m/s. (Take g = 10 m/s²)

The value of 'x' to the nearest integer is __________.

პასუხი
10
24
A bullet of mass 0.1 kg is fired on a wooden block to pierce through it, but it stops after moving a distance of 50 cm into it. If the velocity of bullet before hitting the wood is 10 m/s and it slows down with uniform deceleration, then the magnitude of effective retarding force on the bullet is 'x' N. The value of 'x' to the nearest integer is __________.
პასუხი
10
25
The time period of a simple pendulum is given by $$T = 2\pi \sqrt {{l \over g}} $$. The measured value of the length of pendulum is 10 cm known to a 1mm accuracy. The time for 200 oscillations of the pendulum is found to be 100 second using a clock of 1s resolution. The percentage accuracy in the determination of 'g' using this pendulum is 'x'. The value of 'x' to be nearest integer is :-
პასუხი
(B)
3%
26
A constant power delivering machine has towed a box, which was initially at rest, along a horizontal straight line. The distance moved by the box in time 't' is proportional to :-
პასუხი
(B)
t^3/2
27
What will be the average value of energy along one degree of freedom for an ideal gas in thermal equilibrium at a temperature T? (k_B is Boltzmann constant)
პასუხი
(A)
$${1 \over 2}{k_B}T$$