I am well aware that a charged particle moving in a magnetic field will experience a force perpendicular to that magnetic field. But why is it that positive and negative particles experience a force in opposite directions?
What exactly determines the direction that a given charge will experience a force? I.e. why does a negative particle experience a force in one direction and not the other?
Best Answer
The problem with the why in your question is that it will give rise to another why in the explanation to explain why that explanation occurs and so on; giving rise to an infinite number of whys. But to kick things off, I'll try and give an initial explanation:
Charges deflect in a magnetic field dependent upon their charge sign because of:
We can move to a laboratory moving at the same instantaneous velocity as the charge where it now appears stationary. Any magnetic field here cannot affect the charge because it's not moving; leaving only an electric field, if any, that can affect it. This electric field will deflect that the charge in one of two ways depending upon its sign, which will also be seen in one of two ways in the original laboratory where the charge was moving.
Now we're left with another two questions which I can't give an answer to: