Magnetism and magnetic effects of electric current

The Earth's magnetic field is completely

The Earth's magnetic field is completely described by three elements: (1) Magnetic declination (D) - the angle between magnetic meridian and geographi

Defined as the product of pole

Defined as the product of pole strength (q_m) and magnetic length (2l), expressed as p_m = q_m × 2l. It's a vector quantity pointing from south to nor

The force between two magnetic poles

The force between two magnetic poles is directly proportional to the product of their pole strengths and inversely proportional to the square of dista

For a short bar magnet (r

For a short bar magnet (r >> l): (1) Along axial line: B_axial = (μ₀/4π) × (2p_m/r³), pointing from S to N, and is stronger; (2) Along equatorial line

A magnetic dipole in uniform field

A magnetic dipole in uniform field experiences torque τ = p_m × B sin θ (vector form: τ = p_m × B). This torque tends to align the dipole with field.