Answer: doubles.
- A halves
- B doubles
- C becomes four times
- D is unchanged
Correct answer: B. doubles
Explanation: r = mv/qB, so r ∝ v; doubling the speed doubles the radius.
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.