A current in a wire creates a magnetic field around the wire. You can show this by passing a wire vertically through a hole in a piece of horizontal card and connecting the wire to a power supply. Place plotting compasses on the card, or sprinkle iron filings on it and tap the card gently. The compass needles turn, and the filings line up, to show the shape of the field.
The field lines around a long straight wire are concentric circles centred on the wire. The field is not a set of straight lines pointing towards or away from the wire.
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 direction of the conventional current, and your curled fingers show the direction of the field. If the current is reversed, the compass needles turn round and the direction of the field reverses.
