Transformers: Moving Power Without Moving Parts

By Cliff Potts, CSO, and Editor-in-Chief of WPS News

Baybay City, Leyte, Philippines — August 21, 2026 — 12:30 p.m.

If relays are one of the noisiest components in electronics, transformers are among the quietest.

A relay announces its presence with a click.

A transformer usually says nothing at all.

Yet transformers are among the most remarkable devices ever developed.

Unlike a motor, a transformer has no moving parts.

Unlike a relay, nothing opens or closes.

Unlike a battery, nothing is consumed.

Instead, a transformer quietly transfers electrical energy from one circuit to another using nothing more than magnetism.

That almost sounds impossible.

Fortunately, we have already learned the science behind it.

Several weeks ago, we discovered that electricity creates magnetism.

Then we learned that changing magnetic fields can produce electricity through induction.

A transformer combines those two discoveries into one elegant machine.

Inside a transformer are two separate coils of wire wrapped around a common magnetic core.

The first coil, called the primary winding, receives alternating current.

As the alternating current changes direction, it produces a constantly changing magnetic field.

That changing magnetic field passes through the iron core.

When it reaches the second coil, called the secondary winding, it induces a new electrical current.

No wire connects the two windings.

The electricity never crosses from one winding to the other.

Only the changing magnetic field makes the journey.

That is one of the reasons transformers are so useful.

They provide electrical isolation while still transferring energy.

The next remarkable feature is voltage conversion.

If the secondary winding contains more turns of wire than the primary winding, the output voltage increases.

This is called a step-up transformer.

If the secondary winding contains fewer turns, the output voltage decreases.

This is called a step-down transformer.

The principle is surprisingly simple.

The number of turns determines the voltage relationship.

Because of this property, transformers became one of the most important inventions in electrical engineering.

Electric power plants generate electricity.

Transformers increase the voltage for transmission across long distances.

Higher voltage means lower current for the same amount of power, reducing energy losses in transmission lines.

Near homes and businesses, additional transformers reduce the voltage again to safe operating levels.

Without transformers, modern electrical distribution would be extremely inefficient.

The same principle appears inside electronic equipment.

Many older radios contained power transformers that converted household line voltage into the voltages required by vacuum tubes.

Audio equipment often uses transformers to match circuits together.

Isolation transformers improve electrical safety during servicing.

Even tiny switching power supplies found in modern electronics usually contain miniature transformers operating at much higher frequencies than those used on household power lines.

Electronic Archaeology Note

One of the wonderful things about transformers is that they seem almost magical until you understand induction.

Once you understand induction, the mystery disappears.

The transformer becomes another example of nature following consistent rules.

Electricity creates magnetism.

Changing magnetism creates electricity.

Repeat the process continuously, and energy moves from one circuit to another without any direct electrical connection.

That realization is one of the great moments in learning electronics.

Author’s Note

When I first learned about electronics, transformers fascinated me. The idea that a changing waveform in one coil could induce energy in another coil felt almost impossible. Even more interesting, the waveform itself matters. A sharp pulse or sawtooth-shaped signal can produce a very different response than a smooth sine wave, including high-voltage effects in the secondary winding. We will come back to that later, but it was one of the first things that made transformers feel less like components and more like machines made out of invisible motion.

A transformer also teaches an important lesson about efficiency.

No transformer is perfect.

Some energy is always lost as heat.

The iron core experiences magnetic losses.

The copper windings have electrical resistance.

Engineers spend enormous effort reducing these losses because even small improvements become significant when multiplied across millions of transformers operating every hour of every day.

Despite these losses, transformers remain among the most efficient electrical devices ever built.

Large utility transformers often exceed 98 percent efficiency.

That is an astonishing achievement.

The transformer also illustrates an important limitation.

It requires a changing magnetic field.

That means ordinary transformers work with alternating current, or AC.

Connect a transformer directly to a steady direct current source, and very little happens after the initial connection.

No changing magnetic field means no continuing induction.

This distinction between alternating current and direct current will become increasingly important as our course continues.

It explains why some circuits require one type of electricity while others require the other.

It also explains why power supplies exist.

A transformer can reduce household voltage.

Another circuit can then convert alternating current into direct current suitable for electronic equipment.

That will be our next subject.

For now, remember the transformer for what it truly is.

A silent machine with no moving parts that made the modern electrical world practical.

Without transformers, the electric power grid would look very different.

Without transformers, many of the radios, televisions, amplifiers, and communications systems of the twentieth century would never have operated.

They are quiet.

They are dependable.

They are one of the greatest engineering inventions ever produced.

Next week we will explore the device that combines many of the ideas we have already learned.

The power supply.

It brings together transformers, rectifiers, capacitors, and regulation to create the electricity modern electronics actually needs.

If this work helps you understand what’s happening, help me keep it going: https://www.patreon.com/cw/WPSNews

For more from Cliff Potts, see https://cliffpotts.org

References

Horowitz, P., & Hill, W. (2015). The Art of Electronics (3rd ed.). Cambridge University Press.

Encyclopaedia Britannica. (2025). Transformer. Encyclopaedia Britannica. https://www.britannica.com/technology/transformer-electrical-engineering

U.S. Department of Energy. (n.d.). Fundamentals Handbook: Electrical Science. U.S. Department of Energy.