Electromagnetism Electromagnetism

The primary coil of a step-up
transformer has fewer loops
than the secondary coil. So the
voltage of the electric current
in the secondary coil is higher
than the voltage of the electric
current in the primary coil.
Therefore, voltage is increased.
The primary coil of a stepdown
transformer has more
loops than the secondary coil.
So the voltage of the electric
current in the secondary coil
is lower than the voltage of
the electric current in the primary
coil. Therefore, voltage
is decreased.
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Chapter 18
Transformers Another device that relies on electromagnetic
induction is a transformer. A transformer increases or decreases
the voltage of an alternating current. A simple transformer
consists of two coils of wire wrapped around an iron ring.
Alternating current from an electrical energy source is supplied
to one coil, called the primary coil. The electric current
makes the ring an electromagnet. But the electric current in
the primary coil is alternating, so the magnetic field of the
electromagnet changes with every change in electric current
direction. The changing magnetic field in the iron ring induces
an electric current in the other coil, called the secondary coil.
Step-Up, Step-Down The number of loops in the primary
and secondary coils of a transformer determines whether it
increases or decreases the voltage. If a transformer increases
voltage, it is a step-up transformer. If a transformer decreases
voltage, it is a step-down transformer. Both kinds of transformers
are shown in Figure 26.
Figure 26 Transformers can either increase or decrease voltage.
Primary coil Secondary coil
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