Two particles move into a magnetic field. They enter moving at the same speed and direction. The magnitude of the charge on each is known to be the same. One particle curls to the right and the other to the left upon entering the field, the one on the left moving in a larger circle than the one on the right. From this we can say that
A) the leftward moving particle has more mass and is positively charged.
B) the rightward moving particle has less mass and is positively charged.
C) the leftward moving particle has more mass and its charge is opposite the other particle.
D) the rightward moving particle has positive charge but we cannot say anything about its mass.

Question

Quizplus · Accepted Answer

The fact that the particles curl in opposite directions upon entering the magnetic field indicates they have opposite charges, due to the force exerted by the magnetic field being dependent on the charge's sign. The particle moving in a larger circle has more mass because, for a given charge and velocity, a more massive particle experiences less acceleration and thus moves in a larger circle according to the centripetal force equation $F = \frac{mv^2}{r}$, where $F$ is the magnetic force, $m$ is the mass, $v$ is the velocity, and $r$ is the radius of the circle.

Two Particles Move into a Magnetic Field