How Are Electromagnets Used in TV Screens?

Vintage TVs, like this one, used electromagnets.

Before plasma and liquid-crystal displays (LCD) became popular, the cathode ray tube (CRT) was an essential part of every TV screen. Electromagnets at the base of the CRT steer an electron beam back and forth, producing an image on the screen.

CRT

Inside the CRT's glass envelope, a hot filament produces an electron beam in a vacuum. The beam makes a phosphor screen glow, producing a picture.

Yoke

A set of electromagnets surround the neck of the CRT in a round bracket called a yoke. The variable magnetic fields from the electromagnets produce deflection in the electron beam, causing it to bend.

Scanning

The controlled bending of the electron beam scans the screen with two motions, across and back horizontally, and up and down vertically. This continuously creates the TV picture from a series of thin lines.

Electronics

Electronic circuits in the TV control the electromagnets in the yoke. The circuits provide the exact timing to produce image after image in rapid succession, creating moving images.

Adjustment

The electronic circuits controlling the electromagnets must be carefully adjusted. Otherwise, the image may be too big or small, tilted or warped at the top and bottom.

References

• Warren-Wilson College: Magnetic Deflection
• University of Illinois at Chicago: Cathode Ray Tube
• KSL Technical Portal: TV Servicing Tips