Pattern 1: "Does magnetic force do work?" (NEET 2019, 2023)

• Setup: Charge moves in B; question asks about work done or change in KE
• Trap: Students think force → work; forget F ⊥ v
• Answer: Work = 0; KE constant; speed unchanged; only direction changes
• Key quote: "Magnetic force is always perpendicular to velocity"

Pattern 2: Biot-Savart / Circular Loop Numericals (NEET 2020, 2022)

• Setup: Given N, R, I → find B at centre or on axis
• Formula: B_centre = μ_{0}NI/(2R); B_axis = μ_{0}N$IR^{2}$/[2($R^{2}$+$x^{2}$)^(3/2)]
• Common numbers: N = 100, R = 10 cm, I = 2 A → B = 4π × 10^{-4} T ≈ 1.26 mT
• Trap: Forgetting N (number of turns) in formula; using diameter instead of radius

Pattern 3: Time Period in Magnetic Field (NEET 2018, 2021)

• Setup: Speed of particle changes; "what happens to T?"
• Answer: T = 2πm/(qB) — no v term → T unchanged
• Trap: Students pick "T halves if speed doubles" — WRONG

Pattern 4: Galvanometer Conversions (NEET 2018, 2021)

• Setup: Given G, I_g → find S for ammeter range I, or R for voltmeter range V
• Formulas: S = I_gG/(I − I_g); R = V/I_g − G
• Trap: Mixing up which is parallel (S) and which is series (R)
• Check: Ammeter R_eff ~ S (very small); Voltmeter R_eff = G + R (very large)

Pattern 5: Force Between Parallel Wires (NEET 2017, 2020)

• Setup: Two wires with given currents and separation
• Formula: F/l = μ_{0}$I_{1}I_{2}$/(2πd); same direction → attract
• Trap: Thinking opposite-direction currents attract (they repel!)

Pattern 6: Magnetic Materials Classification (NEET 2019, 2022)

• Setup: Given χ or μᵣ value → identify material class
• Key: χ < 0 = diamagnetic; 0 < χ << 1 = paramagnetic; χ >> 0 = ferromagnetic
• Trap: μᵣ < 1 (not 0) for diamagnetic; μᵣ = 1 + χ

High-Yield NEET Traps Summary