Answer: 1:2.
- A 1:2
- B 2:1
- C 1:1
- D 1:4
Correct answer: A. 1:2
Explanation: r = mv/(qB). m<sub>alpha</sub> = 4m<sub>p</sub>, q<sub>alpha</sub> = 2q<sub>p</sub>. r<sub>alpha</sub> = 4m<sub>p</sub> x v/(2q<sub>p</sub> B) = 2r<sub>p</sub>. Ratio r<sub>p</sub>:r<sub>alpha</sub> = 1:2.
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.