Answer: v = E/B.
- A v = E/B
- B v = B/E
- C v = EB
- D v = E + B
Correct answer: A. v = E/B
Explanation: For straight-line motion: electric force qE = magnetic force qvB. So v = E/B (velocity selector condition).
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.