Which way do field lines point?

The idea

Magnetic field has direction and magnitude; its direction is the way a compass north pole moves, so field lines leave the north pole, enter the south pole and run south to north inside the magnet, forming closed curves.

A compass near a magnet

A small compass is placed near the north pole of a bar magnet. Its red end is the north pole of the needle.

Outside the magnet, which way do the field lines run?

• From the north pole of the magnet to its south pole
• From the south pole of the magnet to its north pole
• They do not point in any direction

Follow the needle

Press Next step. Watch where the red end of the compass points and where the lines go.

Round and round

At every point the red end of a compass points along the field line. We take that as the direction of the field. Outside the magnet, the lines go from the north pole to the south pole. Inside, they go from the south pole to the north pole, so each line is a closed curve.

Magnetic field has direction and magnitude. Its direction is the way a compass north pole moves, so field lines leave the north pole, enter the south pole and run south to north inside the magnet, forming closed curves.

Notes

Field lines leave the north pole, enter the south pole, and run from south to north inside the magnet. They are closed curves.

Check yourself

The direction of the magnetic field at a point is the direction in which…

Outside a bar magnet, field lines…

Inside a bar magnet the field lines run from…

Why are magnetic field lines closed curves?

• the south pole of a compass needle moves. By convention the direction is that in which a north pole moves, not a south pole.
• the iron filings roll. Iron filings only show the pattern of the lines. The direction is the way a north pole of a compass needle moves.
• the north pole of a compass needle moves — correct. Yes!
• emerge from the north pole and merge at the south pole — correct. Yes!
• emerge from the south pole and merge at the north pole. That is the direction inside the magnet. Outside, the lines emerge from the north pole.
• go round the middle of the magnet without touching either pole. Field lines emerge from the north pole and merge at the south pole.
• the north pole to the south pole. That is the direction outside the magnet. Inside, the lines run from the south pole to the north pole.
• the south pole to the north pole — correct. Yes!
• the middle of the magnet out to both ends. Inside the magnet the lines run from the south pole to the north pole.
• They stop at the south pole and start again at the north pole. The lines do not stop at the south pole. Inside the magnet they continue from the south pole to the north pole.
• They leave the magnet and do not return. The lines return through the magnet, from the south pole to the north pole.
• Outside they go from north to south and inside from south to north, so each line joins up — correct. Yes!