JEE Main · Physics ↓ Falling

Magnetism and Matter appeared 9 times across 3 years — 1% of Physics. This question is from Magnetic Monopoles.

Year 2026 2025 2024 Total
Questions 2 6 1 9
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Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason(R). Assertion (A): Magnetic monopoles do not exist. [cite: 138] Reason (R) : Magnetic field lines are continuous and form closed loops. [cite: 138] In the light of the above statements, choose the most appropriate answer from the options given below: [cite: 139]

Solution & Explanation

Core Logic

According to Gauss's Law for Magnetism, the net magnetic flux out of any closed surface is identically zero (∮ B · d A = 0). This directly establishes that magnetic poles always occur in equal and opposite pairs (North and South), meaning isolated magnetic monopoles do not exist[cite: 138]. Because every line of magnetic field entering a region must also leave it, these lines are continuous and closed loops[cite: 138]. The non-existence of monopoles is precisely why the field lines form continuous closed paths rather than diverging from or terminating at standalone single pole points[cite: 138]. Both statements are true and (R) provides the definitive causal explanation for (A)[cite: 143, 725].

Pattern Recognition

Contrast this directly with electrostatics where isolated electric charges do exist, allowing electric field lines to be open lines originating or ending on individual charges.

Chapter Mix

Class 12 Physics: Magnetism and Matter

Reference Study Guides

Magnetism And Matter

More Magnetism and Matter Previous-Year Questions — Page 2

Q17 jee_main_2025_29_jan_evening Magnetic Quantities and Units
Match List-I with List-II. array|l|l|l|l| List-I & & List-II & (A) & Magnetic induction & (I) & Ampere meter² (B) & Magnetic intensity & (II) & Weber (C) & Magnetic flux & (III) & Gauss (D) & Magnetic moment & (IV) & Ampere meter array Choose the correct answer from the options given below:
  • A. (A)-(III), (B)-(IV), (C)-(I), (D)-(II)
  • B. (A)-(III), (B)-(IV), (C)-(II), (D)-(I)
  • C. (A)-(I), (B)-(II), (C)-(III), (D)-(IV)
  • D. (A)-(III), (B)-(II), (C)-(I), (D)-(IV)

Solution

Related Formula
Magnetic Flux: Φ = B · A Weber Magnetic Intensity: H = (B)/(μ) Ampere/meter
Core Logic

Analyzing official units:

  • (A) Magnetic induction arrow Gauss (CGS unit) arrow (III)
  • (B) Magnetic intensity arrow Ampere/meter arrow (Note: List-II text erroneously says "Ampere meter" or missing solidus bar, actual standard is A· m⁻¹) arrow (IV)
  • (C) Magnetic flux arrow Weber arrow (II)
  • (D) Magnetic moment arrow Ampere meter² arrow (I)

    • Due to typo variants in option strings on the primary list sheet, this question was technically dropped by NTA. If picking the closest appropriate intended layout configuration, option (2) presents the best approximation.

Pattern Recognition

Note that this question was officially declared dropped by NTA due to printing formatting discrepancies in the unit labels.

Chapter Mix

Class 12 Physics: Magnetism and Matter

Q10 jee_main_2025_28_jan_evening Magnetic Field of a Bar Magnet
A \bar magnet has total length 2l = 20 units and the field point P is at a distance d = 10 units from the centre of the magnet. If the relative uncertainty of length measurement is 1% , then uncertainty of the magnetic field at point P is:
Magnetic Field of a Bar Magnet diagram for Q10 - JEE Main 2025 Evening
A schematic mapping out the total \bar magnet layout alongside position coordinate node P.
  • A. 10%
  • B. 4%
  • C. 3%
  • D. 5%

Solution

Related Formula

The standard expression for the magnetic field B on the axial path at distance r from the magnetic center is given by :

B ∝ (1)/(r³)

Through logarithmic error differentiation:

(Δ B)/(B) = 3 · ((Δ r)/(r))
Core Logic

Depending on how the evaluation tracks parameter variables, two interpretations arise:

Method 1 (Approximating without considering variations in independently) [cite: 708, 709]: If the spatial uncertainty is tied entirely to the radial component variable r :

(Δ B)/(B) = 3 × 1% = 3%

Method 2 (Accounting comprehensively for dimensional dependencies) [cite: 714, 715]: If the error accumulation bounds combine tracking lengths alongside parameters:

(Δ B)/(B) = (Δ )/( ) + 3((Δ r)/(r)) = 1% + 3(1%) = 4%

Both paths offer distinct structural insights depending on assumptions. The official valuation matrix accepts options reflecting both interpretations.

Pattern Recognition

In general engineering error evaluations, always look at power exponents. If an expression depends inversely on a cubed distance variable, fractional variation scales up by three \times the independent tracking variance.

Chapter Mix

Class 11 Physics: Units and Measurements Class 12 Physics: Magnetism and Matter

Q55 jee_main_2024_29_jan_morning Magnetic Dipole
The magnetic potential due to a magnetic dipole at a point on its axis situated at a distance of 20 ~cm from its center is 1.5 × 10⁻⁵ ~T · m. The magnetic moment of the dipole is ________ A · m². (Given: μ₀4 π = 10⁻⁷ ~T · m · A⁻¹)$
Numerical Answer. Answer: 6 to 6

Solution

Related Formula

The magnetic potential (V) at an axial location at distance r from the center of a magnetic dipole is given by:

V = (μ₀)/(4π) (M)/(r²)

where M represents the magnetic moment.

Core Logic

Given values:

V = 1.5 × 10⁻⁵ ~T · m r = 20 ~cm = 0.2 ~m (μ₀)/(4π) = 10⁻⁷ ~T · m · A⁻¹
Step 1: Set up the Formula

Substituting values into the axial expression:

1.5 × 10⁻⁵ = 10⁻⁷ × (M)/((0.2)²) 1.5 × 10⁻⁵ = 10⁻⁷ × (M)/(0.04)
Step 2: Isolate and Compute M
M = 1.5 × 10⁻⁵ × 0.0410⁻⁷M = 0.06 × 10⁻⁵10⁻⁷ = 0.06 × 10² = 6 ~A · m²

Therefore, the magnetic moment of the dipole is

Therefore, the magnetic moment of the dipole is $6 \mathrm{~A \cdot m^2}.

Pattern Recognition

Axial potential fields scale inversely with the square of distance (

Pattern Recognition

Axial potential fields scale inversely with the square of distance ($V \propto \frac{1}{r^2}$), analogous to electrostatic dipole potentials. Ensure the distance is converted directly to meters before squaring.

Chapter Mix

Class 12 Physics: Magnetism and Matter

More Magnetism and Matter Questions — jee_main_2025_07_april_evening

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