Exam Notes
Magnetic Effects Of Current Class 12 Physics Revision — Grandmaster Guide
A
Ayush (Founder)
Exam Strategist
Last Updated: 2026-06-01
- B = μ₀nI
- F = ILB s∈θ
- F = qvB s∈θ
- τ = nIBA s∈θ
- μ = IA/(NB)
- B = μ₀I/(2πr)
- L = μ₀n²Aℓ
- E = -N(dΦₙ/dt)
- Φ = BA cosθ
- Φₙ = ∫B · dA
- μ = μ₀μᵣ
- μᵣ = 1 + χ
- B = μH
- H = B/μ
- χ = μᵣ - 1
- I = neAVₜ
- Vₜ = √(3kₜT/m)
- I = Q/t
- Q = neVₜA
- Fₘ = Fₗ × B
- Fₗ = qvB
- R = μℓ/(2πr)
- L = μN²A/ℓ
- U = (1/2)LI²
- P = VI
- P = I²R
- E = IR
- V = IR
- R = V/I
- Xₗ = ωL
- Z = √(R² + Xₗ²)
- I = V/Z
- P = VI cosφ
🪤 The 5 Mistakes That Cost Marks
- Not using the correct formula for magnetic field due to a current carrying wire
- Forgetting to consider the direction of the magnetic field
- Not using the right-hand rule to determine the direction of the magnetic field
- Not considering the effect of the magnetic field on the motion of a charged particle
- Not using the correct units for the magnetic field and other related quantities
✏️ 3 Solved PYQs
- A current of 5A is flowing ∈ a wire of length 2m, the magnetic field at a distance of 0.1m from the wire is
- B = μ₀I/(2πr) = (4π × 10⁻⁷ × 5)/(2π × 0.1) = 10⁻⁵ T
- A coil of 100 turns, each of area 0.1m², is placed ∈ a magnetic field of 0.1T, the flux through the coil is
- Φ = BA cosθ = 0.1 × 0.1 × cos0° = 0.01 Wb
- A charged particle of mass 10⁻²⁶ kg and charge 1.6 × 10⁻¹⁹ C is moving ∈ a magnetic field of 0.1T with a velocity of 10⁵ m/s, the force on the particle is
- F = qvB s∈θ = 1.6 × 10⁻¹⁹ × 10⁵ × 0.1 × s∈90° = 1.6 × 10⁻¹⁴ N
🧠 The One Thing Most Students Get Wrong
- The direction of the magnetic field, students often forget to use the right-hand rule to determine the direction of the magnetic field, this can lead to incorrect answers and loss of marks
- The right hand rules states that if you point your thumb ∈ the direction of the current, your fingers will curl ∈ the direction of the magnetic field
- This rule can be used to determine the direction of the magnetic field due to a current carrying wire, a coil, or a solenoid
👁️ Ayush's Note
- To solve problems related to magnetic effects of current, first identify the type of problem, whether it is related to the magnetic field, force, or flux
- Then, use the relevant formula and apply the right-hand rule to determine the direction of the magnetic field
- Make sure to consider the units of the quantities involved and use the correct values for the constants
- Practice problems regularly to develop problem-solving skills and to learn how to apply the concepts to different situations
🔁 Last 5 Minutes Box
- Revision of key concepts and formulas
- Practice of quick calculations and derivations
- Review of common mistakes and how to avoid them
- Focus on the most important topics and questions
- Use of mnemonics and other memory aids to recall key concepts and formulas
📝 Practice MCQs
1. What is the magnetic field at a distance of 0.1m from a wire carrying a current of 5A?
A) 10⁻⁵ T
B) 10⁻⁶ T
C) 10⁻⁷ T
D) 10⁻⁸ T
Answer: A) 10⁻⁵ T, using the formula B = μ₀I/(2πr)
2. A coil of 100 turns, each of area 0.1m², is placed ∈ a magnetic field of 0.1T, what is the flux through the coil?
A) 0.01 Wb
B) 0.1 Wb
C) 1 Wb
D) 10 Wb
Answer: A) 0.01 Wb, using the formula Φ = BA cosθ
3. A charged particle of mass 10⁻²⁶ kg and charge 1.6 × 10⁻¹⁹ C is moving ∈ a magnetic field of 0.1T with a velocity of 10⁵ m/s, what is the force on the particle?
A) 1.6 × 10⁻¹⁴ N
B) 1.6 × 10⁻¹³ N
C) 1.6 × 10⁻¹² N
D) 1.6 × 10⁻¹¹ N
Answer: A) 1.6 × 10⁻¹⁴ N, using the formula F = qvB s∈θ
4. What is the self-inductance of a coil of 100 turns, each of area 0.1m² and length 0.1m?
A) 10⁻⁶ H
B) 10⁻⁵ H
C) 10⁻⁴ H
D) 10⁻³ H
Answer: B) 10⁻⁵ H, using the formula L = μN²A/ℓ
5. A current of 2A is flowing ∈ a wire of length 1m, what is the magnetic field at a distance of 0.05m from the wire?
A) 2 × 10⁻⁵ T
B) 4 × 10⁻⁵ T
C) 6 × 10⁻⁵ T
D) 8 × 10⁻⁵ T
Answer: B) 4 × 10⁻⁵ T, using the formula B = μ₀I/(2πr)
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📚 Academic References
Content verified against peer-reviewed research:
- Mixed approaches to achieve autonomous robot mission tasks using ... — theses.fr (ABES) (2025) 🔓 — DOI ↗
- JSE 34:2 Summer 2020 Whole Issue PDF — Journal of Scientific Exploration (2020) 🔓 — DOI ↗
- Raising Awareness of Artificial Intelligence for Transportation S... — Rosa P: A digital library for transportation research (United States Department of Transportation) (2019) 🔓 — DOI ↗
🔓 = Open Access article
This post was curated by Jules, Exam Compass Bot, and edited for accuracy by Ayush.
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