Name(s) _______________________________
ELECTROMAGNETIC INDUCTION
Purpose
The purpose of this experiment is to help you become familiar with some of the principles of
electromagnetic induction.
Apparatus
Two wire coils
Galvanometer
one rectangular magnet
one soft-iron magnet
33 ohm resistor
9V battery
Theory
Electromagnetic induction theory predicts a voltage any time that there is a change in the amount
of magnetic field within a current loop.
Procedure
Figure 1
We will observe electromagnetic induction using a coil of wire, a permanent magnet and a
galvanometer (a meter that detects small currents or voltage).
1.
Connect the galvanometer to one of the coils, as shown in Figure 1. Watch the
galvanometer while you move the north pole of a magnet through the coil. Answer the
following questions and explain the results.
What is the direction of the galvanometer deflection when you move
a. the north pole of the magnet into the stationary coil?
b. the coil away from the stationary magnet?
c. both toward each other?
2. Watch the galvanometer while you move the south pole of a magnet through the coil.
Answer the following questions and explain the results.
What is the direction of the galvanometer needle when you move
a. the south pole of the magnet into the stationary coil?
b. the coil toward the stationary magnet?
c. both toward each other?
3. When is the coil detecting a changing magnetic field?
4. With the same circuit, place the permanent magnet in the center of the coil, as shown in
Figure 2. The coil now has the maximum amount of magnetic field lines going through
it. Answer the following questions and explain the results.
Figure 2
a. What is the galvanometer reading?
b. How do you account for this reading?
c. Observe the galvanometer while you withdraw the magnet from the coil at constant velocity.
Describe what you observe.
d. Observe the galvanometer while you push the magnet into the coil at constant velocity.
Describe what you observe.
e. Vary the speed with which you withdraw the magnet from the coil. Does this influence how
much current is produced in the coil? Explain.
From the preceding experiments, you should be convinced that it is not the magnetic field, but
the change in magnetic field that produces a voltage across the coil. If we had a method to
change the magnetic field through the coil rapidly, we would be able to generate a sizable
current. We can do this by substituting an electromagnet for the permanent magnet.
5.
Attach the larger diameter coil to a galvanometer. Place the smaller diameter coil
inside the larger coil. Attach the smaller diameter coil in series to a 30 ohm resistor, a
switch, and a 10 volt battery. Make sure the switch is open until your circuit is checked.
The smaller coil connected to the 10 volt battery is called the primary coil while the coil
connected to the galvanometer is called the secondary coil.
Draw a circuit diagram for your two coils here:
a. Observe the galvanometer as you open and close the switch. What happens? Explain.
b. Keep a steady D.C. current through the electromagnet. What is the galvanometer reading?
Explain.
c. Insert a piece of soft iron half way into the smaller coil and repeat steps a and b. Describe
what happens. Explain.
d. How could you use an AC current in the primary coil to induce a current in the secondary
coil?
From what you have observed, describe how induction would occur in each of the following
circuits. (A, B)
A
B