The current in the first coil flows steadily. Which statement about the nearby second coil is correct?
Three demonstrations have each induced an EMF: a magnet moving in a coil, a wire sweeping across a magnetic field, and a neighboring coil at the instant its current switches. Three different setups. Is there one rule behind them all?
In the first, the magnet moves past the coil: relative motion.
In the second, the wire moves through the field between the poles: relative motion again.
In the third, nothing moves. But at switch-on, the magnetic field through the second coil changes.
Each demonstration changes the field through the conductor, or moves one past the other.
One condition covers all three: an EMF is induced whenever the magnetic field through a conductor changes, or there is relative motion between the conductor and the field.
Each demonstration is one way of meeting that one condition.
A magnet spins on a motor's shaft next to a stationary coil. Why is an EMF induced in the coil?
An EMF is induced whenever there is relative motion between the conductor and the field, or the field through the conductor changes.
The spinning magnet moves past the stationary coil.
The magnet and the coil are in relative motion, so an EMF is induced in the coil.
An electromagnet's current is being turned up, and a loop of wire rests beside it. Why is an EMF induced in the loop?
A rising current makes the electromagnet's field grow.
So the magnetic field through the loop is changing.
The field through the loop is changing, so an EMF is induced in the loop.
A magnet swings toward a coil. Is an EMF induced while it swings?
An electromagnet's current is falling. Is an EMF induced in a loop resting beside it?
A moving magnet, a swept wire, and a switched neighboring coil all induce an EMF. What do the three have in common?
Your turn
A loop of wire is dropped past a magnet resting on a shelf. Why is an EMF induced in the loop?
In which situation is an EMF induced?
Which statement gives the condition for an EMF to be induced in a conductor?