A particle with a negative charge is moving south in a magnetic field that points directly downward. In which direction is the magnetic force on the particle?

The direction of the magnetic force on a charged particle moving in a magnetic field can be determined using the right-hand rule. Here are the steps:

1. Point your right thumb in the direction of the particle's motion (south in this case).
2. Point your right index finger in the direction of the magnetic field (downward in this case).
3. Now, curl your remaining fingers. If the particle is positively charged, they will point in the direction of the magnetic force.

However, in this case, the particle is negatively charged. For negative charges, the force is in the opposite direction to the one given by the right-hand rule.

So, if you did the above steps correctly, your palm should be facing east. But since the charge is negative, the force is in the opposite direction, which is west.

Therefore, the magnetic force on the particle is directed towards the west.