A compass needle always points north, but near a wire with a current it swings away. In this course we map the field of a magnet with field lines, we find that a current has a magnetic field too, and we use a coil to make an electromagnet that we can switch on and off.
3 lessons, about 1 h 20 min3 simulations12 problems6 practice questionsPython in every lesson
Created by StemPy LabA magnet has a north pole and a south pole. Like poles repel and unlike poles attract. The region around a magnet in which it acts is its magnetic field. We draw the field with field lines: outside the magnet they go from the north pole to the south pole, they are closer where the field is stronger, and they never cross.
A wire that carries a current has a magnetic field around it. This was found by Oersted. The field lines of a straight wire are circles around it, and their direction is given by the right-hand thumb rule. The field is stronger when the current is larger, and weaker when the distance from the wire is larger. At the centre of a circular loop the field is straight, and a coil of many turns gives a stronger field.
A solenoid is a long coil of many turns of wire. Its field is like the field of a bar magnet: strong and uniform inside, with one end a north pole and the other a south pole. A soft iron core inside it makes an electromagnet. This strong magnet can be switched on and off, and its strength changes with the current and the number of turns.
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