Magnetic forces on moving charges

What you’ll practice

Build confidence with the Lorentz force F = q(v × B), including how charge sign flips direction and how speed and field strength affect magnitude. You’ll also connect particle motion (helical/circular paths) to real setups like velocity selectors and magnetic bending.

Expect a balanced mix of conceptual checks and light math: units, proportional reasoning, and right-hand-rule direction choices. The quiz uses 4 options per question and no timer, so you can slow down and verify your reasoning.

Common pitfalls to avoid

Mixing up v × B direction, forgetting the sign of q, or assuming the force is along the field are the most frequent errors. Another trap is using sin/cos incorrectly when velocity is not perpendicular to the magnetic field.

How difficulty and length work

Difficulty is mixed by design: easier items reinforce core rules, while harder ones combine geometry, components, and motion relationships. Before you start, pick your question count and a difficulty setting to tailor the session - short for review, longer for full coverage.

Quick tips for better scores

• Use the right-hand rule for v × B first, then reverse if the charge is negative
• Remember: magnetic force is perpendicular to velocity, so it changes direction more than speed
• For angles, use |F| = |q|vB sin(θ) and check whether θ is between v and B
• In uniform B with v ⟂ B, motion is circular; with a parallel component, it becomes helical
• Track units: tesla (T), coulomb (C), m/s, and newton (N)
• When stuck, test each option against direction and proportionality (double v → double F)