If a conducting rod moves through a magnetic field which way do its electrons move?
In my revision guide it shows the following picture (more or less, but the following is my drawing of it — I didn't change anything):
I'm having trouble understanding why the electrons accumulate on the end of the rod shown in the picture. Surely by Fleming's left hand rule the flow of positive charge will be in the direction of the green arrow here:
Which means that the electrons flow in the opposite direction to the green arrow, so the "plus" and "minus" signs in the rod are the wrong way round in this diagram. It should be like:
Or am I doing something wrong?
Thanks!
Best Answer
Let us imagine that the charge carriers in the rod are electrons (negatively charged). An electron moving to the right is equivalent to a (conventional) current to the left. Alternatively, you can use a "left hand rule" for electrons (since the current is to the left when the motion is to the right, you can represent electron motion with the thumb of your left hand, or conventional current with the right hand).
Either way - with your right hand thumb pointing to the left, and your index finger pointing down, your middle finger is pointing towards you: so that is where the force of the magnetic field is pushing the electrons, and that is why the negative charge accumulates on the side of the rod facing you.
Your mistake was in looking at the divided charges and concluding there will be a current along the wire; as long as the rod is moving at a steady rate through a homogeneous magnetic field, there will be no flow along the rod (after the charge has split as shown).