Field lines do not cross
A needle cannot point two ways.
Crossing lines
Imagine drawing the field lines around a magnet. A friend draws two of them so that they cross each other at a point.
What is wrong with the friend's picture?
What this lesson covers
The idea
No two magnetic field lines cross, since at a crossing point a compass needle would have to point in two directions, which is not possible.
Crossing lines
Imagine drawing the field lines around a magnet. A friend draws two of them so that they cross each other at a point.
What is wrong with the friend's picture?
- A compass at the crossing would have to point in two directions
- The lines are too close together
- Field lines may not be drawn longer than the magnet
Why not cross?
Press Next step to see what a crossing would mean for a compass needle.
One point, one direction
At a point in a magnetic field, a compass needle points in one direction only. A crossing of two lines would ask for two directions at that point. That cannot happen, so field lines do not cross.
No two magnetic field lines cross, because at a crossing point a compass needle would have to point in two directions, which is not possible.
Notes
No two field lines cross: at a crossing a compass needle would have to point in two directions, which is not possible.
Check yourself
Why can two magnetic field lines not cross each other?
A compass needle is placed at one point in a magnetic field. How many directions does it point in?
Which statement about magnetic field lines is correct?
- A compass needle at the crossing would have to point in two directions — correct. Yes!
- The lines would then be too close together. Closeness of lines shows a stronger field. Lines do not cross because a needle cannot point in two directions at once.
- A field line must stay inside the magnet. Field lines run outside the magnet, from the north pole to the south pole. They do not cross because a needle cannot point in two directions.
- Two, one along each of two crossing lines. Field lines do not cross, so only one line passes through the point and the needle points in one direction.
- One — correct. Yes!
- It points in no direction. A compass needle placed in a magnetic field points along the field line through that point.
- Field lines cross where the field is strongest. Strength is shown by how close the lines are. Field lines do not cross.
- Two field lines cross at the north pole of the magnet. Field lines emerge from the north pole. No two of them cross.
- No two field lines cross each other — correct. Yes!