Chapter 12 Electromagnetic Induction
233
Summary
• Voltage can be induced in a coil of wire
either by passing a magnet through the
coil or by holding the magnet stationary
and moving the coil over it.
• Voltage can be induced in a wire by
changing the magnetic fi eld.
• An inductor is a device that resists a
change in current.
• Inductance is a measurement of how
much an inductor opposes current
change.
• Inductance is affected by the number
of turns of wire in a coil, the type of
core, the cross-sectional area of the core,
and the length of coil compared to the
number of turns of wire.
• When two coils of wire are close enough
to be linked by a magnetic fi eld, they are
said to have mutual inductance.
• The formula for mutual inductance is
M = K
√L1L2.
____
• Transformers use the principle of mutual
inductance to increase or decrease the
amount of voltage and current in a
circuit.
• The ratio between the numbers of turns
equals the ratio between the voltages in
the primary and secondary windings of
a transformer:
N
P
___
N
S
=
E
P
___
E
S
Test Your Knowledge
Do not write in this book. Write your answers on
a separate sheet of paper.
1. Voltage created by a changing magnetic
fi eld cutting through a coil is called
______.
2. The opposition to a change in current
fl ow is called ______.
3. An inductor will have no effect on ______
circuits.
4. The part of a circuit that opposes a
change in current is called a(n) ______.
5. Draw the symbols for a fi xed and
variable inductor.
6. The unit of inductance is the ______.
7. Name three things that affect the
inductance of a coil.
8. If we had three inductors connected in
series, each having a value of 4 mH, what
would the total inductance be? Show
your work.
9. Name the two windings found on a
transformer.
10. Is ac or dc produced in the secondary
winding of a transformer?
11. Laminations on the core of a transformer
help cut down on the ______ loss.
12. The two types of transformers that get
their name from how they affect the
voltage are ______ and ______.
13. A transformer connected to a 120-V ac
source has 400 turns on the primary
winding. If we want to obtain 6 V from
the second winding, how many turns
of wire do we need for the secondary?
Show your work.