How Does Removing a Card Affect Currents in Parallel Wires?

[Peter G.]

Hi,

Question: There are two long, parallel vertical wires, each carrying currents in the same direction. The wire passes through a horizontal sheet of card.

The card is removed and one of the two wires is free to move. Describe and explain the changes in velocity, and in acceleration of the moveable wire.

Answer: Well, so, I believe that, since there is an attractive force between both of the wires, if the card is removed, the moveable wire will move towards the second wire. This means that there is a change in velocity of the wire, an acceleration, that increases as the moveable wire moves towards the second wire due to the fact the field is stronger closer to the wire.

Is that what they want?

Thanks,
Peter G.

 

[technician]

Sounds good to me. Test yourself... what would happen if the currents in each wire were in opposite directions?

 

[Peter G.]

Ah ok, got it! If the currents in the wire were in opposite directions, the force would be repulsive. If one wire were allowed to move, the velocity would still increase but the acceleration decrease gradually. Now however, I have to answer why field lines never cross. Well, from what I understand, the field lines indicate direction and their spacing indicate their strength. So, if two field lines crossed they would have infinite force?

 

[technician]

That is what I would say also.
The reason field lines can't cross? Field lines basically show a Force direction. If they crossed then there would be a choice of 2 different directions at the crossing point and that does not happen.