Cathode ray tube Facts for Kids

A cathode ray tube using electromagnetic focus and deflection

The cathode ray tube or CRT was a very common type of screen for many years. It was used in almost all computer monitors and televisions. You would have seen CRTs in older, bulky TVs before LCD and plasma screens became popular.

What is a Cathode Ray Tube?
History of the Cathode Ray Tube
Related pages
Images for kids
See also

What is a Cathode Ray Tube?

A CRT is a special kind of vacuum tube. It has a part called an electron gun. This gun shoots out tiny particles called electrons.

How the Electron Gun Works

The electron gun has a cathode. This is a metal part that gets hot. When it heats up, it sends out electrons. Inside the glass tube, there's also an anode. This anode is like a magnet for electrons. It pulls the electrons towards the front of the tube. This makes the electrons shoot out in a straight line, creating a "cathode ray."

Creating a Vacuum

To make sure the electrons travel in a straight line without hitting air molecules, all the air is taken out of the tube. This creates a vacuum.

Making the Picture Glow

The electrons hit the front of the tube, which is covered with a special material called phosphor. When electrons hit the phosphor, it lights up.

Controlling the Image

You can aim the electrons by using a magnetic field. By carefully controlling where the electrons hit the phosphor, a bright picture appears on the screen. If this picture changes very quickly, about 30 times every second, it looks like the picture is moving. This is how old TVs and computer monitors showed videos.

Why CRTs Were Heavy

Because there's a vacuum inside, the glass tube had to be very strong and thick. This was to stop the outside air pressure from crushing it. That's why large CRT televisions were often very heavy!

History of the Cathode Ray Tube

The cathode ray tube was invented in 1897 by Karl Ferdinand Braun. At first, it was used in a machine called an oscilloscope. An oscilloscope shows waves, like sound waves or electrical signals.

Later, in the 1920s, the CRT was used by Philo T. Farnsworth to create the first modern electronic television. For many decades, the CRT was the main type of screen for TVs. However, in the early 2000s, liquid crystal display (LCD) screens became popular. They were much thinner and lighter, and soon replaced CRTs in most homes.

Images for kids

A cathode-ray tube as found in an oscilloscope
Cutaway rendering of a color CRT: 1. Three electron emitters (for red, green, and blue phosphor dots) 2. Electron beams 3. Focusing coils 4. Deflection coils 5. Connection for final anodes (referred to as the "ultor" in some receiving tube manuals) 6. Mask for separating beams for red, green, and blue part of the displayed image 7. Phosphor layer (screen)with red, green, and blue zones 8. Close-up of the phosphor-coated inner side of the screen
The rear of a 14-inch color cathode-ray tube showing its deflection coils and electron guns
Typical 1950s United States monochrome television set
Snapshot of a CRT television showing the line of light being drawn from left to right in a raster pattern
Animation of the image construction with interlacing method
Color computer monitor electron gun
Braun's original cold-cathode CRT, 1897
Small circular CRTs during manufacture in 1947 (screens being coated with phosphor)
A portable monochrome CRT TV
A Trinitron CRT computer monitor
A monochrome CRT as seen inside a TV. The CRT is the single largest component in a CRT TV.
A monochrome CRT as seen inside a Macintosh Plus computer
An aluminized monochrome CRT. The black matte coating is aquadag.
The deflection yoke over the neck of a monochrome CRT. It has two pairs of deflection coils.
Magnified view of a delta-gun shadow mask color CRT
On the left: Magnified view of In-line phosphor triads (a slot mask) CRT. On the right: Magnified view of Delta-gun phosphor triads.
Magnified view of a Trinitron (aperture grille) color CRT. A thin horizontal support wire is visible.
Spectra of constituent blue, green and red phosphors in a common CRT
The in-line electron guns of a color CRT TV
A degaussing in progress
Mu metal magnetic shields for oscilloscope CRTs
The front of a Sony Watchman monochrome CRT
A flat monochrome CRT assembly inside a 1984 Sinclair TV80 portable TV
An oscilloscope showing a Lissajous curve
The electron gun of an oscilloscope. A pair of deflection plates is visible on the left.
The Tektronix Type 564: first mass-produced analog phosphor storage oscilloscope
Nimo tube BA0000-P31
A comparison between 21-inch Superslim and Ultraslim CRT
A monochrome CRT with 110° deflection
A monochrome CRT with 90° deflection
Older monochrome CRT without aluminum, only aquadag
The electron gun of a monochrome CRT
The side of a Sony Watchman monochrome CRT. One of the pairs of deflection coils is easily noticeable.