Answer: speed.
- A speed
- B direction
- C velocity
- D momentum direction
Correct answer: A. speed
Explanation: The magnetic force does no work, so it changes direction but not speed.
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.