Radius of circular motion in a magnetic field
A proton and an electron enter the same uniform magnetic field at the same speed, perpendicular to the field. Which moves in the larger circle?
Answer D: explanation for every choice
A
A smaller mass gives a smaller radius.
B
Equal charge magnitude isn't enough. Mass also sets the radius.
C
Charged particles moving perpendicular to a field travel in circles.
D
Correct. r = mv/(|q|B). With equal |q|, v, and B, the radius scales with mass, and the proton is about 1,836 times heavier.
Takeawayr = mv/(|q|B). They also circle in opposite directions.
Equation usedMagnetic force on a moving charge
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