An electric current creates a magnetic field around the wire carrying it. You can show this with a plotting compass. Place the compass next to a straight wire, then switch the current on. The needle deflects (moves) away from its normal north-pointing position. Switch the current off and it swings back. This shows that a current has a magnetic effect.
Around a long straight wire the field forms concentric circles centred on the wire, in a plane at right angles to the wire. Placing compasses around the wire shows the needles pointing along these circles.
The direction of the field depends on the direction of the current. Use the right-hand grip rule: point the thumb of your right hand along the conventional current, and your fingers curl in the direction of the field. If the current is reversed, the field is reversed too, so the compass needles turn to point the opposite way.
