Cathode ray tube Facts for Kids

Cathode ray tube using electromagnetic focus and deflection

The cathode ray tube or CRT was invented by Karl Ferdinand Braun. It was the most common type of display for many years. It was used in almost all computer monitors and televisions until LCD and plasma screens started being used.

A cathode ray tube has an electron gun. The cathode is an electrode (a metal that can send out electrons when heated). The cathode is inside a glass tube. Also inside the glass tube is an anode that attracts electrons. This is used to pull the electrons toward the front of the glass tube, so the electrons shoot out in one direction, making a cathode ray. To better control the direction of the ray, the air is taken out of the tube, making a vacuum.

The electrons hit the front of the tube, where a phosphor screen is. The electrons make the phosphor light up. The electrons can be aimed by creating a magnetic field. By carefully controlling which bits of phosphor light up, a bright picture can be made on the front of the vacuum tube. Changing this picture 30 times every second will make it look like the picture is moving. Because there is a vacuum inside the tube (which has to be strong enough to hold out the air), and the tube must be glass for the phosphor to be visible, the tube must be made of thick glass. For a large television, this vacuum tube can be quite heavy.

The cathode ray tube was invented in 1897, and used as an oscilloscope (a machine to show waves). Later, along with other inventions and improvements, it was used for the first modern electronic television by Philo T. Farnsworth in the 1920s. The CRT was the main type of television screen until the liquid crystal display became popular in the early 2000s.

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.

Cathode ray tube facts for kids

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