Home » JEE Main Physics Magnetic Effects of Current and Magnetism

JEE Main Physics Magnetic Effects of Current and Magnetism

Update on: 03 Jan 2023, 02:30 PM

JEE Main Physics Magnetic Effects of Current and Magnetism

Many important questions are formed in competitive exams like CUET, JEE, NEET, and boards from Class 12 Physics Unit  3. Below, we have provided Important Questions from Class 12 Physics Unit 3 Magnetic Effects of Current and Magnetism for your JEE Mains 2023 preparation. You can check it here for revision purposes.

Latest: Electrostatics Class 12 JEE Questions and Answers

Electrostatics Class 12 JEE Mains Questions and Answers

We’ve compiled a list of important questions about the Magnetic Effects of Current and Magnetism physics class 12 unit 3 that you should not miss while studying for your JEE Main Exams.

Q.1. 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

A.1. (b)


ratio of the magnetic field













Q.2. 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 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

A.2. (d)

Q.3.  In a hydrogen atom, the electrons moves in a circular orbit of radius 0.5 Å, about the nucleus. 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

A.3. (c)


magnetic induction produced









Q.4. 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

A.4. (c)


Answer 4










Q.5. 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 radius 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

A.5. (b)


Answer 5






Q.6.  A B and C are parallel conductors of equal lengths carrying currents I, I and 2I respectively. Distance between A and B is x. 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

A.6. (d)


Answer 6









Q.7. 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 loop
(c) shape of loop (d) strength of current and magnetic field

A.7. (c)

Q.8. A coil of N turns and radis 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

A.8. (b)


Answer 8










Q.9. 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

A.9. (d)


Answer 9









Q.10. 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

A.10. (b)


Answer 10

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