Video Transcript
The diagram below shows a bar
magnet and a copper ring. The copper ring is stationary,
while the bar magnet is rotating. Will a current be induced in the
copper ring?
To answer this question, let’s
start by recalling that when a loop of conducting wire is exposed to a changing
magnetic field, a potential difference is induced in the wire. And this potential difference
generates a current in the wire. This is electromagnetic
induction. To think about how to answer this
question though, let’s first imagine a stationary copper ring on its own with no
magnets around it. The ring isn’t connected to any
kind of circuit, and there’s nothing else near the ring. So, there is no current in this
ring because there is nothing that could cause the charges in the ring to flow.
Now consider what would happen if
we placed a stationary bar magnet next to the ring. In this case, there is still no
current in the ring, but some of the bar magnet’s magnetic field lines now pass
through the ring, like this. However, if the magnet or ring
started to move with respect to each other, then the magnetic field that passes
through the ring would change, which would induce a current in the wire. In this question, we’re considering
a bar magnet that’s rotating. Rotating the bar magnet would in
turn rotate the magnetic field produced by the magnet, which would definitely cause
the magnetic field passing through the ring to change.
We’ve already established that when
a loop of wire is exposed to a changing magnetic field, current will be induced in
the wire. So, the answer to this is therefore
yes. When the magnet rotates, a current
will be induced in the copper ring.
