Answer: zero.
- A zero
- B positive
- C negative
- D a maximum
Correct answer: A. zero
Explanation: The force is perpendicular to the velocity, so it does no work on the charge.
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.