Magnetic Fields & Magnetic Force — A/L Physics

What must I remember about Magnetic Fields & Magnetic Force?

• Magnetic Field (B): Region of space wherein moving charges, electric currents, or magnetic dipoles experience magnetic forces; measured in Tesla (T = N·A⁻¹·m⁻¹ = Wb/m²).
• Lorentz Force Equation: Total electromagnetic force acting on charge q moving with velocity v: F = q (E + v × B); Magnetic Force component: F_B = q (v × B) = q v B sin θ.
• Properties of Magnetic Force: Perpendicular to both velocity v and magnetic field B (determined by Fleming's Left-Hand Rule or vector right-hand cross rule); zero force when particle moves parallel to field (θ = 0° or 180°); magnetic force does ZERO work on moving charge (speed and kinetic energy remain strictly constant).
• Magnetic Force on Current-Carrying Conductor: Conductor of length L carrying current I in magnetic field B experiences force: F = I (L × B) = B I L sin θ.

Test yourself (1 minute)

1. Charged particle trajectory in uniform magnetic field

   Injected perpendicular (θ = 90°): executes Uniform Circular Motion with radius r = (m v) / (q B) and cyclotron frequency f = (q B) / (2π m); Injected at angle θ: executes Helical path with pitch p = v_parallel * T = (2π m v cos θ) / (q B).

2. Velocity Selector

   Crossed uniform electric field E and magnetic field B (E ⊥ B); particles passing undeflected satisfy q E = q v B => v = E / B, regardless of charge or mass.

3. Torque on Current Loop

   Rectangular coil of N turns and area A carrying current I in magnetic field B: Torque τ = N I A B sin θ = m × B, where magnetic dipole moment m = N I A n̂.

Practise Magnetic Fields & Magnetic Force questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 8: Electromagnetism

What should I study first?

What comes next?

Next in the syllabus

Where does Magnetic Fields & Magnetic Force fit in the syllabus?

Unit 8.1 · Year 2 · Term 1