4 mistakes learners make with electromagnetism, each one named and explained.
A magnetic field fills the space around a magnet, and it pushes on moving charge rather than on charge sitting still.
You say a magnet held near a wire will push the electrons along, with no current flowing.
A magnet acts on a current-carrying wire, so it seems it should act on the charges in any wire.
Question. A magnet is held beside a wire carrying no current. What force acts on the electrons?
A common answer. a force pushing them along the wire
The answer. none, because a magnetic field only pushes on charge that is moving
Why. The motor effect needs a current. No current means no movement, and no force.
Look for a current first. No current, no motor effect.
You say the coil must be stripped of its coating so the electricity can get through.
Insulation is the thing that stops current, so it looks like it would stop the electromagnet working.
Question. Should the wire wound into an electromagnet coil be bare or insulated?
A common answer. bare, so the current can flow
The answer. insulated, so the current is forced around every turn
Why. Bare turns touching each other let the current cut across the coil instead of going round it.
More turns means more field only if the current goes round all of them.
You explain a magnet attracting a nail and a charged rod attracting paper as the same effect.
Both act at a distance, both attract small objects, and neither can be seen.
Question. A charged plastic rod picks up small pieces of paper. Is that magnetism?
A common answer. yes, it is the same force as a magnet
The answer. no, it is an electrostatic effect, a different field
Why. Magnets act on magnetic materials and moving charge; charge acts on charge.
Ask what is being pulled. Charge and iron are not the same thing.
You draw field lines as two tufts at the ends of the magnet, with nothing in between.
The poles are where a magnet grips hardest, and where iron filings crowd most thickly.
Question. Where is there a magnetic field around a bar magnet?
A common answer. only at the two poles
The answer. everywhere around it, strongest near the poles
Why. Field lines run from one pole right round to the other, so the field fills the space.
Draw complete loops from pole to pole. A field line never simply stops.
WAJD spots these patterns in your child's answers and names the one behind their wrong answers, instead of just marking them wrong.