Magnetic Effects of Electric Current — Formula Sheet

$B$: Magnetic field (tesla, T) · $I$: Current in the wire (A) · $r$: Perpendicular distance from wire (m)

Field forms concentric circles around a long straight wire. Stronger with more current, weaker farther away.

Grip the wire with the right hand, thumb along current — fingers curl in the direction of B.

At the centre of a loop of radius r. For N turns, B becomes N × (that value).

${\mu }_0$: Permeability of free space = 4π × 10⁻⁷ T·m/A · $n$: Number of turns per metre (m⁻¹) · $I$: Current in the solenoid (A)

Uniform field inside a long solenoid. n = turns per unit length. Field pattern is like a bar magnet.

Maximum when B ⊥ I. Direction given by Fleming's LEFT-hand rule.

Stretch thumb, forefinger and middle finger of LEFT hand mutually perpendicular — gives force direction. Basis of the electric MOTOR.

RIGHT hand: thumb (motion), forefinger (field), middle (induced current). Basis of the GENERATOR.

An EMF is induced in a coil whenever the magnetic flux linked with it changes. Faster the change, larger the EMF.

In India: V = 220 V AC, 50 Hz. Fuse rating chosen slightly above the appliance's normal current I = P/V.