Magnetic Effects JEE Main Questions 2025: Important Practice Questions with PYQs

Q1:  A straight wire of length π2 metre carrying a current of 2 A and the magnetic field due to it is measured at a point distant 1 cm from it. If the wire were bent into a circle and were to carry the same current as before, the ratio of the magnetic field at its centre to that obtained in the first case would be:
(a) 50: 1 (b) 1: 50

(c) 100: 1 (d) 1: 100

Q2: A bar magnet has a magnetic moment equal to 5 × 10–5 Wb m. It is suspended in a magnetic field which has a magnetic induction B equal to 8p × 10–4 T. The magnet vibrates with a period of vibration equal to 15 s. The moment of inertia of a magnet is

(a) 4.54 × 104 kg m2 (b) 4.54 × 10–5 kg m2
(c) 4.54 × 10–4 kg m2 (d) 4.54 × 105 kg m2

Q3:  In a hydrogen atom, the electrons move about the nucleus in a circular orbit of radius 0.5 Å. What is the magnetic induction produced at the centre of the orbit, if the electrons make 6.25 × 1015 rev per sec? [e = 1.6 × 10–19 C]

(a) 6.28 Wb m–2 (b) 9 Wb m–2

(c) 12.56 Wb m–2 (d) 15 Wb m–2

Q4: A solenoid of length 0.4 m and having 500 turns of wire carries a current of 3.0 A. A thin coil having 10 turns of wire and of a radius of 0.01 m carries a current of 0.04 A. What is the torque required to hold the coil in the middle of the solenoid with its axis perpendicular to the axis of the solenoid? (Use π2 = 10)

(a) 6 × 106 N m (b) 6 × 10–6 N m
(c) 7.5 × 10–6 N m (d) 4.2 × 10–6 N m

Q5: There is a uniform electric field of strength 103 Vm–1 along the y-axis. A body of mass 1 g and charge 10–6 C is projected into the field from the origin along the positive x-axis with a velocity of 10 ms–1. Its speed (in ms–1) after 10 s will be (negative gravitation)

(a) 10 (b) 5√2 (c) 10√2 (d) 20

Q6:  A B and C are parallel conductors of equal lengths carrying currents I, I and 2I respectively. The distance between A and B is x. The distance between B and C is also x. F1 is the force exerted by B on A. F2 is the force exerted by conductor C on A. Choose the correct answer.

(a) F1 = 2F2 (b) F2 = 2F1

(c) F1 = F2 (d) F1 = –F2

Q7: The magnetic susceptibility of a paramagnetic material at –73°C is 0.0075 and its value at –173°C will be

(a) 0.0030 (b) 0.0075

(c) 0.0045 (d) 0.015

Q8: A long straight wire of radius R carries a current I. The current is uniformly distributed across its cross-section. What is the ratio of the magnetic fields at distances of R/2 and 2R from its axis?

(a) 1/2
(b) 1
(c) 2
(d) 4

Q9:  A coil of N turns and radius R carries a current I. it is unwound and rewound to make another coil of radius R/2, current remaining the same. What is the ratio of the magnetic moments of the new coil and the original coil?

(a) 1: 1 (b) 1: 2 (c) 2: 1 (d) 1 : 3

Q10: A current-carrying loop is placed in a uniform magnetic field. The torque acting on it does not depend upon

(a) area of loop (b) no. of turns in the loop

(c) shape of loop (d) strength of current and magnetic field

Q1: Given below are two statements :

Statement (I): When currents vary with time, Newton's third law is valid only if momentum carried by the electromagnetic field is taken into account

Statement (II): Ampere's circuital law does not depend on Biot-Savart's law.

In the light of the above statements, choose the correct answer from the options given below :

1. Both Statement I and Statement II are false
2. Statement I is false but Statement II is true
3. C) Both Statement I and Statement II are true
4. Statement I is true but Statement II is false

April 9, 2024 (Morning Shift)

Q2:  A long straight wire of radius a carries a steady current I. The current is uniformly distributed across its cross-section. The ratio of the magnetic field at a2 and 2a from the axis of the wire is :

1. 4:1
2. 3:4
3. 1:1
4. 1:4

April 8, 2024 (Evening Shift)

​Q3: An element Delta l= Delta xi^ is placed at the origin and carries a large current  I=10 A. The magnetic field on the y-axis at a distance of    0.5 m from the elements delta x of  1 cm length is:

​

1. 10×10−8 T
2. 8×10−8 T
3. C 4×10−8 T
4. 12×10−8 T

Q4: A straight magnetic strip has a magnetic moment of  44 Am^2. If the strip is bent in a semicircular shape, its magnetic moment will be ________Am^2  given pi= 22/7

Q5: A square loop of edge length  2 m carrying current of 2 A is placed with its edges parallel to the x--y axis. A magnetic field is passing through the x-y plane and expressed as B->=B0(1+4x)k^, where B0=5T, The net magnetic force experienced by the loop is _________ N.

Q7: An electron with kinetic energy 5 eV enters a region of uniform magnetic field of 3uT perpendicular to its direction. An electric field E is applied perpendicular to the direction of velocity and magnetic field. The value of E, so that the electron moves along the same path, is __________ NC-1. (Given, mass of electron = 9×10−31kg, electric charge = 1.6×10−19C)