Formula CheatsheetCBSE & ICSEClass 12PhysicsCh-5Verified Faculty Notes & Solutions
Magnetism- Class 12 Physic Ch-5
Formula Sheet
3 students readUpdated 1 October 2026
Formula Sheet
Class 12 Physics Formula Sheet
Magnetism and Matter — Complete Revision Guide
1. Bar Magnet & Magnetic Dipole
- Magnetic Dipole Moment (M): M = qm × 2l (Where qm = pole strength, 2l = magnetic length. Also M = NIA where N = turns, I = current, A = area. Unit: A·m2)
- Magnetic Field on Axial Line (End-on): B = (μ0 / 4π) × (2Mr) / (r2 - l2)2 (Where M = magnetic moment, r = distance from center, l = half-length. For short magnet, r >> l: B = (μ0 / 4π) × (2M / r3))
- Magnetic Field on Equator Line (Broadside-on): B = (μ0 / 4π) × M / (r2 + l2)3/2 (For short magnet, r >> l: B = (μ0 / 4π) × (M / r3))
- Torque on Bar Magnet: τ [tau] = M × B = MB sin(θ [theta = angle between M and B])
- Potential Energy of Magnetic Dipole: U = -M · B = -MB cos(θ [theta])
- Oscillation Time Period: T = 2π [pi = 3.14] × √(I / (MB)) (Where I = moment of inertia of the magnet, M = magnetic moment, B = magnetic field)
2. Earth's Magnetism (Terrestrial Magnetism)
- Components of Earth's Magnetic Field:
• Horizontal Component: BH = B cos(δ [δ = angle of dip])
• Vertical Component: BV = B sin(δ) - Relations:
• Total Earth Field: B = √(BH2 + BV2)
• Angle of Dip: tan(δ) = BV / BH
3. Magnetic Terms & Material Properties
- Intensity of Magnetization (I): I = M / V = m / A (Where M = magnetic moment, V = volume, m = pole strength, A = cross-sectional area)
- Magnetic Intensity / Magnetizing Field (H): H = B0 / μ0 = nI (Where n = turns per unit length, I = current in solenoid)
- Magnetic Susceptibility (χ [chi]): χ = I / H (Ratio of intensity of magnetization to magnetic intensity)
- Magnetic Permeability (μ): μ = B / H (Where B = total magnetic field inside material)
- Relative Permeability (μr): μr = μ / μ0 = 1 + χ
4. Types of Magnetic Materials
- Diamagnetic Materials: χ is small and negative (-1 to 0), μr < 1. Repelled by magnets (e.g., Bismuth, Copper, Water).
- Paramagnetic Materials:
χ is small and positive, μr > 1. Weakly attracted (e.g., Aluminum, Oxygen).
Curie's Law: χ = C / T (Where T = Absolute temperature in Kelvin, C = Curie constant) - Ferromagnetic Materials:
χ is very large and positive, μr >>> 1. Strongly attracted (e.g., Iron, Cobalt, Nickel).
Curie-Weiss Law: χ = C / (T - Tc) (Where Tc = Curie temperature)
Key Formulas (Most Frequently Used)
- Axial Field: B = (μ0 / 4π) × (2M / r3) (M = magnetic moment, r = distance)
- Equatorial Field: B = (μ0 / 4π) × (M / r3)
- Torque & Potential Energy: τ = MB sin(θ) and U = -MB cos(θ)
- Earth Field & Dip: BH = B cos(δ) and tan(δ) = BV / BH (δ = angle of dip)
- Permeability & Susceptibility: μr = 1 + χ and χ = C / T
Board Important Questions & Derivations
- Derivation 1: Derive expression for magnetic field intensity due to a bar magnet at its axial and equatorial points.
- Derivation 2: Obtain expression for torque and potential energy of a magnetic dipole in a uniform field.
- Conceptual Q: Define magnetic declination and magnetic dip. What are their values at the magnetic poles and equator?
- Distinction Q: Differentiate between diamagnetic, paramagnetic, and ferromagnetic materials using susceptibility (χ) and behavior.
- Law Q: State Curie's law. Explain what happens to a ferromagnetic substance when heated above its Curie temperature.
SixBytes Academic Coaching • Shyampur & Premnagar
Aiming for 95%+ in CBSE / ICSE Board & Competitive Exams?
Join daily batches at SixBytes Institute for personalized mentoring, one-on-one doubt solving, and structured mock test series for Classes 9–12 & NDA.