# electric transformers

## what is an electric transformer

An electric transformer is a device that uses electromagnetic induction to change the voltage of electric current. Electromagnetic induction is the process of generating current with a magnetic field. It occurs when a magnetic field and electric conductor, such as a coil of wire, move relative to one another. A transformer may either increase or decrease voltage. You can see the basic components of an electric transformer in the Figure 1.1. Click image to the left or use the URL below. URL: The transformer in the diagram consists of two wire coils wrapped around an iron core. Each coil is part of a different circuit. When alternating current passes through coil P, it magnetizes the iron core. Because the current is alternating, the magnetic field of the iron core keeps reversing. This is where electromagnetic induction comes in. The changing magnetic field induces alternating current in coil S of the other circuit.

## stepping up or stepping down

Notice that coil P and coil S in the Figure 1.1 have the same number of turns of wire. In this case, the voltages of the primary and secondary currents are the same. Usually, the two coils of a transformer have different numbers of turns. In that case, the voltages of the two currents are different. When coil S has more turns than coil P, the voltage in the secondary current is greater than the voltage in the primary current (see Figure 1.2). This type of transformer is called a step-up transformer. Thats because it steps up, or increases, the voltage. When coil S has fewer turns of wire than coil P, the voltage in the secondary current is less than the voltage in the primary current (see Figure 1.3). This type of transformer is called a step-down transformer because it steps down, or decreases, the voltage. Q: Both step-up and step-down transformers are used in the electrical grid that carries electricity from a power plant to your home. Where in the grid do you think step-down transformers might be used? A: One place that step-down transformers are used is on the electric poles that supply current to homes. They reduce the voltage of the electric current before it enters home circuits.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

electric transformers may either increase or decrease voltage.

``````-->  a. true

b. false
``````

an electric transformer contains

``````a) a single electric circuit.

-->  b) an iron core.

c) a permanent magnet.

d) all of the above
``````

an electric transformer creates an electromagnet when

``````a) alternating current passes through the secondary coil.

b) the magnetic field of the iron core keeps changing.

c) direct current passes through the primary coil.

-->  d) none of the above
``````

the type of transformer in question 7 would be found on an electric pole outside of a home.

``````a. true

-->  b. false
``````

electromagnetic induction occurs in an electric transformer because the

``````-->  a) magnetic field keeps reversing.

b) secondary coil keeps moving.

c) primary coil keeps moving.

d) two of the above
``````

## diagram questions

No diagram questions associated with this lesson