Electricity and magnetism

Where this sits

Comes after

Circuits

Exercises from this rung

Generated by the app, from easiest to hardest

1. You cut the current to an electromagnet. What happens?

   • It stops being a magnet
   • It gets hotter
   • It stays just as strong
   • Its poles swap

   Why It stops attracting at once, and that is exactly what makes it useful: a scrapyard crane lifts a car and drops it without touching anything. The magnetism was made by the current, not by the iron; with no current there is no field.

   easier

2. You put a compass beside a wire carrying current. What does the needle do?

   • It swings aside
   • It stops dead
   • It keeps pointing north
   • It spins without stopping

   Why It swings aside, and that was the whole discovery: in 1820 Ørsted saw a needle move when he switched on a circuit during a lesson and realised that current creates a magnetic field around itself. Electricity and magnetism stopped being two things that day.

   in between

3. You move a magnet inside a coil of wire. What happens?

   • The coil becomes a permanent magnet
   • Nothing happens
   • The magnet loses strength
   • A current appears in the coil

   Why A current appears, with no battery and nothing plugged in, just from moving the magnet. Stop moving it and it stops: what generates current is the **change** in the field, not the field. That is how all the electricity you use is made: a power station is just something spinning magnets inside coils.

   harder