Answer: Half.
- A Doubled
- B Unchanged
- C Quadrupled
- D Half
Correct answer: D. Half
Explanation: Pitch = v cosθ × T where T = 2πm/(qB). Since pitch is inversely proportional to B, doubling B makes the pitch half of its original value.
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.