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Electromagnetic Induction
Electricity is induced in the coil when the number of
magnetic field lines inside the coil changes
In order for electromagnetic induction to occur, the
number of magnetic field lines inside the loop must
change. How can this be done?
There are 3 ways to change the number of magnetic field
lines inside the loop.
• Change the magnetic field, B
• Change the area of the loop (convert to a circle)
• Rotate the loop
Electromagnetic induction occurs when the
loop area in a magnetic field changes (quickly).
The magnetic force (F) due to the induced current (I)
opposes the motion of the rod to the right. If this didn’t
happen, we would have a perpetual motion machine.
Electromagnetic induction occurs when the
loop in a magnetic field is rotated (quickly).
THE BIG PICTURE
Electricity is induced whenever the number of magnetic
field lines inside the loop of wire is quickly changed.
The number of magnetic field lines inside the wire loop
changes when the loop is rotated. The faster this change
occurs, the larger the induced voltage.
Generator Simulation
Generator
Motor
Input
loop rotation
electricity
Output
electricity
loop rotation
Once a generator is producing electricity, it has a motor
effect that tries to spin the loop in the opposite direction
of the input.
Once a motor has loops rotating, it has a generator effect
that induces electricity in the opposite direction of the
input.
The guitar string is magnetized by the pickup magnet.
When the string vibrates, the wire coil experiences a
changing magnetic field. Electricity is produced via
electromagnetic induction.
In a microphone, the magnetic field inside the vibrating
coil rapidly changes. Electromagnetic induction occurs.
Loudspeakers and microphones have the same parts.
Microphone
Loudspeaker
Input
sound
electricity
Output
electricity
sound
In a phono cartridge, when the stylus passes through the
grooves of a record it will vibrate. This causes the magnet
inside the coil to also vibrate. Since there is now a rapidly
changing magnetic field inside the coil, electromagnetic
induction occurs.
Transformers
Transformer - a device for increasing or decreasing voltage
through electromagnetic induction.
Power in equals power out
If the voltage increases, the current must decrease.