What happens to the direction of the magnet field about a straight section of wire when the direction of the current is reversed?

Answer 1

In that case, the magnetic field caused by the current would also be reversed. As for the wire itself, it would feel a force in the opposite direction, due to the interaction of the magnetic fields.

Answer 2

The magnetic force at a point in a magnetic field is always perpendicular to both the current direction that produces that field and the distance vector, r, that defines a point in the field. Hence, reversing the current running though a wire will have the affect of reversing the direction of the magnetic force at a point some distance away from the wire. The affect that this has on the overall magnetic field depends on the shape of the wire. If you made an electromagnet by sending a current through a solenoid (a coiled wire), reversing the current through the wire would reverse that magnetic poles of the electromagnet.

If you ran a current through a simple straight length of wire, the magnetic field lines that describe the field would be concentric circles with the wire as a center point. these circular field lines would run over the length of the wire pointing either clockwise or counter clockwise. Reversing the current in the wire will reverse this clockwise or counterclockwise direction.

To describe the exact affect that reversing the current will have on a particular shape of wire you need to use the this general rule: The direction of the magnetic force at any point is equal to the cross product of a differential current direction and a position vector from the differential segment to that point. Use the following steps to draw the magnetic field lines of the field produced by running a current through any shape of wire:

1) Point the thumb of your right hand in the direction of the current through a small segment of the wire

2) Your four fingers will then sweep out the path of the field lines produced by that segment

3) Repeat this for all small segments of the wire until you have a nice picture of what the overall magnetic field looks like.

If you want to see how changing the current affects the nature of the magnetic field for this given shape of wire, repeat 1-3 above but change the direction of the current. Compare the two drawings that you have made.

Answer 3

The direction of the magnetic field changes according to the right hand rule.