Conventional Current?

Physics Level 2 2.6 Electricity and electromagnetism
1

Hi, I was just wondering if we are supposed to use conventional current flow when finding out the force on a wire moving through a magnetic field?

2

Hi Harry,

If you’re given a situation in which a wire is moving through a magnetic field, using the right hand slap rule, your thumb would indicate the direction of conventional current generated.

Note: you wouldn’t be asked about the current generated if the wire already has a current. If the wire already has a current then you may need to identify the direction of the magnetic field lines, or the direction of force experienced by the wire.

Let me know if you’re using a different rule, or need clarification.

3

Hi Doug,

Thank you for that, however, if I was asked to find the direction of the force on the wire that has a current, should I be using the right hand slap rule to find the force on the ELECTRONS within the wire, or the positive charges (right hand slep rule)? Thanks

4

Hi Harry,

Good question. Using the right hand slap rule, your palm shows the direction of force experienced by positive charges. Your fingers point in the direction of the magnetic filed lines, and your thumb indicates the direction of conventional current.

eg. Imagine a wire was hanging vertically in front of you, and magnetic field lines were directed away from you (forwards). If the conventional current in the wire is directed upwards, the wire would experience a force to your left.

If the wire in front of you was horizontal, the magnetic field lines were pointing towards you, and the conventional current was from your left to right, which directon would the wire experience a force?

5

Hi Doug,

I believe that the wire would be experiencing a force downwards. That is if we are taking about positive charge

So when they ask to find a direction of a force on a wire, they want us to find the force on positive charges, not the actual electrons moving through the wire.

6

That is correct Harry. A question would specifically state ‘electron’, or ‘negatively charged object’, if you were being asked to find a quantity or direction related to negative charge. The right hand slap and grip rules both apply when considering positively charges.