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Part of MAG-01 — Magnetic Effects of Current & Magnetism

Exam Cheat Sheet — All Key Facts for NEET

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FIELD FORMULAS (B in Tesla = [MT^{-2}$$A^{-1}])

SourceFormula
Infinite wireB = μ_{0}I/(2πd)
Circular loop (centre)B = μ_{0}NI/(2R)
Circular loop (axis)B = μ_{0}NIR2IR^{2}/[2(R2R^{2}+x2x^{2})^(3/2)]
Solenoid (inside)B = μ_{0}nI, n = N/L
Toroid (inside ring)B = μ_{0}NI/(2πr)

FORCE FORMULAS

SituationFormula
Moving chargeF = qvB sinθ (⊥ to v; no work)
ConductorF = BIl sinθ
Between parallel wiresF/l = μ_{0}I1I2I_{1}I_{2}/(2πd)
Torque on loopτ = NIAB sinθ = MB sinθ

CIRCULAR MOTION

  • Radius: r = mv/(qB) [depends on v]
  • Period: T = 2πm/(qB) [INDEPENDENT of v — NEET trap!]
  • Frequency: f = qB/(2πm)

GALVANOMETER CONVERSIONS

  • Ammeter: S = I_gG/(I − I_g) in PARALLEL (low resistance)
  • Voltmeter: R = V/I_g − G in SERIES (high resistance)

MATERIALS

  • Dia: χ < 0; μᵣ < 1; Cu, Bi, H2OH_{2}O; repelled; T-independent
  • Para: χ > 0 small; Al, O2O_{2}; attracted; χ = C/T
  • Ferro: χ >> 0; Fe, Co, Ni; strongly attracted; domains; hysteresis

KEY CONSTANTS

  • μ_{0} = 4π × 10^{-7} T·m/A
  • e = 1.6×10−11.6 \times 10^{-1}^{9} C; m_p = 1.67×10−21.67 \times 10^{-2}^{7} kg

NEET MUST-REMEMBER

  1. Magnetic force does NO work (F ⊥ v always)
  2. T = 2πm/(qB) — velocity-independent
  3. Ammeter = PARALLEL shunt (low R); Voltmeter = SERIES R (high R)
  4. Solenoid B depends on n = N/L, not N alone
  5. Above Curie temperature: ferromagnet → paramagnetic

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