Magnetic Effects of Current and Magnetism: One-Page Formula Sheet

Magnetic Effects of Current and Magnetism — formula sheet

Formulas

• Long wire: B = μ₀I / 2πr; circular loop centre: μ₀I / 2R
• Solenoid: B = μ₀nI
• Radius r = mv/qB, period T = 2πm/qB
• Force between wires per length: μ₀I₁I₂ / 2πd

Key ideas

• Magnetic force qv × B does no work
• Charged particle in uniform B moves in a circle or helix
• Parallel currents attract, antiparallel repel
• A galvanometer becomes an ammeter with a shunt and a voltmeter with a series resistance

Traps to avoid

• Wrong direction from the right-hand rule
• Forgetting the field of a semi-infinite wire is half
• Using the solenoid formula near its ends

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