JEE (Main) · Physics, Class 12
Magnetic Effects of Current and Magnetism: JEE Main PYQ, 2020–2025
Magnetic Effects of Current and Magnetism (Physics, Class 12) has been asked 199 times in the 111 JEE (Main) shift papers from 2020–2025: about 1.8 questions a paper, 7% of all Physics questions. It is the 4th most-asked of 20 Physics chapters. The 2025 shifts had 24 from it in all. Last checked 28 October 2026.
Questions per year, all shifts
Year by year.
| Year | Questions |
|---|---|
| 2020 | 27in 14 papers |
| 2021 | 39in 26 papers |
| 2022 | 48in 24 papers |
| 2023 | 22in 12 papers |
| 2024 | 39in 18 papers |
| 2025 | 24in 17 papers |
JEE (Main) is sat in many shifts a year, each with its own paper; the counts add up every shift. 2021–2024 papers had 30 questions a subject, the others 25.
Inside the chapter
Topics asked most.
- Force on moving charges and currents62
- Biot-Savart law33
- Magnetic properties of materials28
- Moving coil galvanometer27
- Magnetic dipole24
- Ampere's law17
- Earth magnetism8
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10 Magnetic Effects of Current and Magnetism questions to practise.
Our own questions, written in the JEE Main pattern and checked, each with an explanation. Pick an option to see the answer.
Q1 · Physics · Magnetic Effects of Current and Magnetism
A very short current element lies at the origin with its current along the +x direction. According to the Biot–Savart law, at which of the following points is the magnetic field due to this element zero?
Answer: (A)
The Biot–Savart law gives dB ∝ I dl sin θ / r², where θ is the angle between the current element and the line joining it to the point. For a point on the line of the element itself, θ is 0° or 180°, sin θ = 0 and the field is zero. Everywhere off that line the element produces a field.
Q2 · Physics · Magnetic Effects of Current and Magnetism
A bar magnet of magnetic moment 1.6 A m² is placed on a horizontal table with its north pole pointing towards geographic north (along the magnetic meridian). The horizontal component of the Earth's field is 2.0 × 10⁻⁵ T. Neutral points, where the net horizontal field is zero, occur on the equatorial line of the magnet. How far from the centre of the magnet are they? Treat the magnet as a point dipole and take μ₀/4π = 10⁻⁷ T m A⁻¹.
Answer: (A)
With the magnet's north pole pointing north, the field on its equatorial line points from north to south, opposite to M. That is the opposite direction to the Earth's horizontal field H (south to north). They cancel where (μ₀/4π)M/d³ = H. So d³ = (10⁻⁷ × 1.6)/(2.0 × 10⁻⁵) = 8.0 × 10⁻³ m³, and d = 0.20 m. If the magnet's north pole pointed south, its axial field (twice as large at the same distance) would oppose H instead, and the neutral points would lie on the axis.
Q3 · Physics · Magnetic Effects of Current and Magnetism
Three identical pieces of thin wire, each of length L, carry the same steady current I. One is bent into a circular loop, another into an equilateral triangle, and the third into a square. What is the ratio of the magnetic dipole moment of the circular loop to that of the equilateral triangular loop?
Answer: (A)
For a planar loop, μ = I·A, and I is the same for all three, so the ratio equals the ratio of areas. Circle: 2πR = L, so R = L/2π and A = πR² = L²/(4π). Equilateral triangle: side s = L/3, so A = (√3/4)(L/3)² = √3L²/36. The ratio is (L²/4π) ÷ (√3L²/36) = 36/(4π√3) = 9/(π√3) = 3√3/π.
Q4 · Physics · Magnetic Effects of Current and Magnetism
A straight wire 10 cm long carrying 2 A lies perpendicular to a uniform magnetic field of 0.5 T. What force acts on it?
Answer: (C)
F = BIL sin θ = 0.5 × 2 × 0.1 × sin 90° = 0.1 N, perpendicular to both the wire and the field.
Q5 · Physics · Magnetic Effects of Current and Magnetism
A very long wire carrying a current I = 5 A is bent into an L shape. One arm lies along the positive x-axis from the origin O to infinity. The other arm lies along the positive y-axis from infinity to O. The current enters along the y-arm and leaves along the x-arm. What is the magnitude of the magnetic field at the point P(−5 cm, 0)? (μ₀/4π = 10⁻⁷ T m A⁻¹)
Answer: (A)
The Biot–Savart law gives dB ∝ I dl × r/r³. For the x-arm, every element and every r vector lie along the x-axis, so dl × r = 0 and this arm contributes nothing at P. For the y-arm, P is at perpendicular distance d = 0.05 m from the foot of the arm at O. One end of the arm is at this foot (angle 0) and the other is at infinity (angle 90°), so B = (μ₀I/4πd)(sin 90° − sin 0°) = μ₀I/(4πd). This gives B = 10⁻⁷ × 5/0.05 = 1.0 × 10⁻⁵ T = 10 μT, which is half the field of an infinite wire.
Q6 · Physics · Magnetic Effects of Current and Magnetism
Two long straight parallel wires are 20 cm apart. They carry currents of 3 A and 5 A in opposite directions. What is the magnitude of the magnetic field at the point midway between them? (μ₀ = 4π × 10⁻⁷ T m A⁻¹.)
Answer: (D)
Each wire gives B = μ₀I / 2πr at r = 0.10 m: 6 × 10⁻⁶ T for 3 A and 1.0 × 10⁻⁵ T for 5 A. By the right-hand rule, antiparallel currents produce fields in the same direction in the region between the wires, so the fields add: B = 1.6 × 10⁻⁵ T.
Q7 · Physics · Magnetic Effects of Current and Magnetism
The magnitude of the magnetic field at a point near a short current element is measured at a perpendicular distance r from it. If this distance is doubled, keeping the current the same, by what factor does the magnetic field change?
Answer: (A)
The Biot–Savart law states that the field from a current element is dB = (μ₀/4π)(I dl sinθ)/r², where r is the distance from the element to the point. The field therefore falls off as the inverse square of the distance. Doubling r gives a factor of (1/2)² = 1/4. Keep the current and the angle fixed; only r changes.
Q8 · Physics · Magnetic Effects of Current and Magnetism
A moving coil galvanometer has a coil of 50 turns and area 2.0 × 10⁻³ m², placed in a radial magnetic field of magnitude 0.040 T. A current of 5.0 mA produces a steady deflection of 30° (π/6 rad). What is the torsional constant of the suspension spring?
Answer: (D)
In a radial field the magnetic torque is NIAB for every position of the coil. The spring's restoring torque is kφ. At equilibrium NIAB = kφ. NIAB = 50 × 5.0×10⁻³ × 2.0×10⁻³ × 0.040 = 2.0×10⁻⁵ N m. With φ = 30° = π/6 rad ≈ 0.524 rad, k = 2.0×10⁻⁵ / 0.524 ≈ 3.8×10⁻⁵ N m rad⁻¹.
Q9 · Physics · Magnetic Effects of Current and Magnetism
A long solenoid with 500 turns per metre carries a steady current of 0.50 A. A soft ferrite rod of relative permeability 400 and cross-sectional area 2.0 × 10⁻⁴ m² fills the central region of the solenoid, with its axis along the solenoid axis. A search coil of 50 turns is wound tightly around the middle of the rod. The search coil is connected to a circuit of total resistance 5.0 Ω. The solenoid current is then reversed (changed to 0.50 A in the opposite direction). Take μ₀ = 4π × 10⁻⁷ T m A⁻¹ and ignore any flux outside the rod. The total charge that flows through the search-coil circuit is closest to:
Answer: (A)
The magnetising field depends only on the free current: H = nI = 500 × 0.50 = 250 A m⁻¹. In the ferrite, B = μ₀μr H = 4π × 10⁻⁷ × 400 × 250 = 4π × 10⁻² T ≈ 0.126 T. The flux through each turn is Φ = BA = 0.126 × 2.0 × 10⁻⁴ ≈ 2.5 × 10⁻⁵ Wb. Reversing the current reverses B, so the change in flux per turn is 2Φ ≈ 5.0 × 10⁻⁵ Wb. The charge that flows is q = NΔΦ/R = 50 × 5.03 × 10⁻⁵ / 5.0 ≈ 5.0 × 10⁻⁴ C.
Q10 · Physics · Magnetic Effects of Current and Magnetism
The current sensitivity of a moving coil galvanometer is defined as:
Answer: (A)
Current sensitivity is the ratio of deflection to the current producing it, S_I = θ/I. Its unit is commonly rad per ampere or division per ampere. A larger value means the galvanometer shows a bigger deflection for the same current, so it is more sensitive. Keep it distinct from voltage sensitivity, which is deflection per volt.
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All 199 real JEE Main questions from Magnetic Effects of Current and Magnetism.
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About Magnetic Effects of Current and Magnetism in JEE Main.
How many questions come from Magnetic Effects of Current and Magnetism in JEE Main?
Magnetic Effects of Current and Magnetism (Physics, Class 12) has been asked 199 times in the 111 JEE (Main) shift papers from 2020–2025: about 1.8 questions a paper, 7% of all Physics questions. It is the 4th most-asked of 20 Physics chapters. The 2025 shifts had 24 from it in all.
Which topics of Magnetic Effects of Current and Magnetism are asked most in JEE Main?
Force on moving charges and currents (62), Biot-Savart law (33), Magnetic properties of materials (28), Moving coil galvanometer (27), counted over the papers from 2020–2025.
Is Magnetic Effects of Current and Magnetism important for JEE Main 2027?
It is in the syllabus in force, so it can be asked. By past papers it ranks 4 of 20 in Physics; use that to decide how much time it gets, not whether to study it.
Where can I solve Magnetic Effects of Current and Magnetism JEE Main previous year questions?
On Nikaalle, free: sign up and practise every past JEE Main question from Magnetic Effects of Current and Magnetism with an explanation for each, or sit the full papers timed. The ten questions on this page are our own, written in the same pattern.
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