# Homework Help: Electric Potential

1. Jun 13, 2010

### ojsimon

Hi

Ok so i came across this question which asks you to find the force on electrons in a wire which is moving in a magnetic field, hence the opposite to the direction of the current. I worked out using The right hand rule that the current would be going from point P to Q, which was write. However the next part asked to find if the potentials of p or q was greater, i said that p was bigger because the definition of potential is the work done per unit charge to bring a small test charge from infinity to that point, hence you would need less work to bring a charge to Q(the negative terminal) than to p (the positive terminal). But the answer says it that the potential of p is less than the potential of q, but gives no explanation. Why is it that the potential of p is less than the potential of Q?

Thanks

2. Jun 13, 2010

### ojsimon

Can no one answer this question?

3. Jun 14, 2010

### rcgldr

From what I understand, potential should be the negative of the work done per unit charge going from P to Q, you don't need an external reference point. I don't understand why the voltage (electric potential) would be less at P than Q in this example. The electrical potential energy of the electrons would be less at P than Q, because it's multiplied by the negative charge of the electrons. This is assuming that there is resistance in the wire and that the voltage at P is higher than the voltage at Q.

Last edited: Jun 14, 2010
4. Jun 17, 2010

### R&AW

hello !
can you be a bit more specific about the details eg how is the wire PQ aligned ? What is the direction of the magnetic field?