Answer: T/3.
- A 3T
- B T
- C T/3
- D T/9
Correct answer: C. T/3
Explanation: The period T = 2πm/(qB) is independent of speed and inversely proportional to B. Tripling B gives a period of T/3.
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.