#Cathode ray television free#

In 1908, Alan Archibald Campbell-Swinton, fellow of the Royal Society (UK), published a letter in the scientific journal Nature, in which he described how 'distant electric vision' could be achieved by using a cathode-ray tube (or 'Braun' tube) as both a transmitting and receiving device. Braun was the first to conceive the use of a CRT as a display device. It was a cold-cathode diode, a modification of the Crookes tube with a phosphor-coated screen. The earliest version of the CRT was known as the 'Braun tube', invented by the German physicist Ferdinand Braun in 1897. Thomson succeeded in measuring the charge-mass-ratio of cathode rays, showing that they consisted of negatively charged particles smaller than atoms, the first ' subatomic particles', which had already been named electrons by Irish physicist George Johnstone Stoney in 1891. In 1890, Arthur Schuster demonstrated cathode rays could be deflected by electric fields, and William Crookes showed they could be deflected by magnetic fields. Hittorf observed that some unknown rays were emitted from the cathode (negative electrode) which could cast shadows on the glowing wall of the tube, indicating the rays were traveling in straight lines. History Discoveries Braun's original cold-cathode CRT, 1897Ĭathode rays were discovered by Julius Plücker and Johann Wilhelm Hittorf. The electrons are steered by deflection coils or plates, and an anode accelerates them towards the phosphor-coated screen, which generates light when hit by the electrons.

Ī CRT works by electrically heating a tungsten coil which in turn heats a cathode in the rear of the CRT, causing it to emit electrons which are modulated and focused by electrodes. Flat-panel displays can also be made in very large sizes whereas 40 in (100 cm) to 45 in (110 cm) was about the largest size of a CRT.

Since the mid-late 2000's, CRTs have been superseded by flat-panel display technologies such as LCD, plasma display, and OLED displays which are cheaper to manufacture and run, as well as significantly lighter and less bulky. CRTs make up most of the weight of CRT TVs and computer monitors. The face is typically made of thick lead glass or special barium-strontium glass to be shatter-resistant and to block most X-ray emissions. As such, handling a CRT carries the risk of violent implosion that can hurl glass at great velocity.

#Cathode ray television free#

The interior is evacuated to 0.01 pascals (1 ×10 −7 atm) to 0.1 micropascals (1 ×10 −12 atm) or less, to facilitate the free flight of electrons from the gun(s) to the tube's face without scattering due to collisions with air molecules. 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 gunĪ CRT is a glass envelope which is deep (i.e., long from front screen face to rear end), heavy, and fragile. Electrostatic deflection is commonly used in oscilloscopes. In modern CRT monitors and televisions the beams are bent by magnetic deflection, using a deflection yoke. In color devices, an image is produced by controlling the intensity of each of three electron beams, one for each additive primary color (red, green, and blue) with a video signal as a reference. In CRT television sets and computer monitors, the entire front area of the tube is scanned repeatedly and systematically in a fixed pattern called a raster. The term cathode ray was used to describe electron beams when they were first discovered, before it was understood that what was emitted from the cathode was a beam of electrons. CRTs have also been used as memory devices, in which case the screen is not intended to be visible to an observer. A CRT on a television set is commonly called a picture tube. The images may represent electrical waveforms ( oscilloscope), pictures ( television set, computer monitor), radar targets, or other phenomena. The only visible differences are the single electron gun, the uniform white phosphor coating, and the lack of a shadow mask.Ī cathode-ray tube ( CRT) is a vacuum tube containing one or more electron guns, which emit electron beams that are manipulated to display images on a phosphorescent screen.