A current turns a compass needle
Electricity and magnetism are linked.
A needle near a wire
A compass needle rests pointing north and south. A copper wire lies just above it. The wire is joined to a battery and a switch, and the switch is closed.
What happens to the needle?
What this lesson covers
The idea
An electric current through a wire produces a magnetic effect, deflecting a nearby compass needle; a current-carrying wire behaves like a magnet, so electricity and magnetism are linked.
A needle near a wire
A compass needle rests pointing north and south. A copper wire lies just above it. The wire is joined to a battery and a switch, and the switch is closed.
What happens to the needle?
- It turns away from its north to south position
- It stays exactly where it was
- It melts
Open and close the switch
Press Next step to see the wire with no current, then with a current.
The wire acts like a magnet
With the switch open, nothing happens to the needle. When a current flows, the needle turns. A needle is a small magnet, so the wire must be acting like a magnet. This is called the magnetic effect of electric current. Experiments like this are done by a teacher in the lab with a small battery.
An electric current through a wire produces a magnetic effect, deflecting a nearby compass needle. A current-carrying wire behaves like a magnet, so electricity and magnetism are linked.
Notes
A current-carrying wire behaves like a magnet: it deflects a compass needle, so electricity and magnetism are linked.
Check yourself
A compass needle near a wire is deflected when a current flows in the wire. What does this show?
Which statement is correct about a wire that carries a current?
Which of these is a MAGNETIC effect of an electric current?
What did the accidental discovery of Oersted in 1820 show?
- The wire has become hot and pushed the needle. Heating is another effect of current, studied in the chapter on electricity. The needle is deflected by the magnetic effect of the current.
- The current in the wire has produced a magnetic effect — correct. Yes!
- The compass needle was already broken. A compass needle is a small magnet that can be deflected. Here the current in the wire is what produced the deflection.
- It behaves like a plain piece of copper that cannot affect a compass. The needle is deflected by a current-carrying wire, so the wire does affect a compass.
- It behaves like a magnet only when the compass is far away. A compass deflected near the wire shows the magnetic effect; a far away compass is not the way to show it.
- It behaves like a magnet — correct. Yes!
- A nearby compass needle is deflected — correct. Yes!
- A fuse wire melts when too much current flows. Melting of a fuse wire comes from Joule heating, which is the heating effect of current.
- A wire gets warm when a current flows through it. Getting warm is the heating effect of current. The deflected compass needle is the magnetic effect.
- Compass needles are made of copper. Oersted's observation was about a current deflecting a compass needle. It showed that electricity and magnetism are related.
- Electricity and magnetism are related phenomena — correct. Yes!
- A battery is needed to make a compass needle. A compass needle is a small bar magnet. Oersted showed that a current-carrying wire placed nearby deflects it.