Answer: v = E/B.
- A v = B/E
- B v = EB
- C v = E²/B
- D v = E/B
Correct answer: D. v = E/B
Explanation: For the particle to move undeflected, the electric force qE must balance the magnetic force qvB, giving v = E/B; this principle is used in velocity selectors.
The magnetic field around a long straight current-carrying wire forms concentric circles, with direction given by the right-hand rule (point thumb along I, fingers curl in the direction of B).
Concept context
Magnetic force on moving charges and currents, the Biot-Savart law, Ampere's law, and the cyclotron - how electric currents create and respond to magnetic fields.