See here (AQA)
There are various types. CRT (Cathode Ray Tube) now on its way out, replaced by LCD (Liquid Crystal Display) and TFT (Thin Film Transistor) screens
Advantages: TFTs light and flat, CRTs may be hazardous to health (largely replaced by LCDs)
Disadvantages: overuse may strain eyes
The carthode ray tube (CRT) is a vacuum tube containing an electron gun (a source of electrons) and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. (Wikipedia)
The CRT uses an evacuated glass envelope which is large, deep (i.e. long from front screen face to rear end), fairly heavy, and relatively fragile. As a matter of safety, the face is typically made of thick lead glass so as to be highly shatter-resistant and to block most X-ray emissions, particularly if the CRT is used in a consumer product. (Wikipedia)
They are far lighter and thinner than traditional television sets and video displays that use cathode ray tubes (CRTs), and are usually less than 10 centimetres (3.9 in) thick. They can be divided into two general display technology categories: volatile and static. (Wikipedia)
"A thin layer of liquid crystal, a liquid that exhibits crystalline properties, is sandwiched between 2 electrically conducting plates.The top plate has transparent electrodes deposited on it, and the black plate is a mirror. By applying proper electrical signals across the plates, various segments of the liquid crystal can be activated, causing changes in their light diffusing or polarizing properties. These segments can either transmit or block light. An image is produced by passing light through selected segments of the liquid crystal and then reflected it back from the mirror to the viewer. They are used in various electronics like watches, calculators, and notebook computers." (Wikipedia)
Liquid crystals can change the polarisation state of light when an electrical field is applied to them. They can be used with a light source and polarising filters to control the amount of light reaching a screen. A LCD screen is a matrix of liquid crystal cells, each representing one pixel when the screen is at full resolution. To make a colour display each pixel is divided into 3 or 4 sub-pixels with colour filters for additive mixing of R, G & B; there may also be a grey pixel for brightness control. Flat screens work best at their native resolution, when it is equal to the number of pixels - which is whjy laptop screens have fixed resolutions in line with the number of pixels they contain and why it is best to set a flat screen to its native resolution.
Thin film transistor (TFT) is another flat screen technology. Each pixel consists of a TFT, a capacitor and a liquid crystal. The transistor is a switch to turn current on and off while the capacitor stores the el;ectrical field to charge the liquid crystal. The capacitor holds its charge until the next referesh cycle.
They are far lighter and thinner than traditional television sets and video displays that use cathode ray tubes (CRTs), and are usually less than 10 centimetres (3.9 in) thick. They can be divided into two general display technology categories: volatile and static. (Wikipedia) They use less power than CRT screens and are not refreshed in the same way so there is no flicker. There is no projection system so screen geometry is perfect - no distortion at the edges of the screen.
A plasma display consists of two glass plates separated by a thin gap filled with a gas such as neon. Each of these plates has several parallel electrodes running across it. The electrodes on the two plates are at right angles to each other. A voltage applied between the two electrodes one on each plate causes a small segment of gas at the two electrodes to glow. The glow of gas segments is maintained by a lower voltage that is continuously applied to all electrodes. A similar pulsing arrangement is used to selectively turn points off. (Wikipedia)
Plasma panels are well suited to large displays e.g. 50 inch TVs and bigger, though LCD displays in these sizes have now been successfully built. Each pixel is controlled by a miniature fluorescent ligtht; when electrical charge is applied the gas becomes plasma and emits ultraviolet light, which strikes phosphors on the screen and produces light. They have a wider viewing angle than LCD screens.
Plasma uses more electricity due to the need to referesh the charge on each pixel: if charge is lost the colour reduces and contrast is lost. For this reason they generate a lot of heat and are expensive to run (and not very 'green'). Pixel size is larger than LCD so is unsuitable for use with small monitors designed for close viewing - hence its use in large TVs designed for large rooms and not in computer monitors.
For all printer types identify suitable uses and features such as purchase costs, running costs, quality of output and speed.
Various types including laser, ink-jet and dye-sublimation. Laser is fast and good for text so is popular in offices. Ink-jet is slow and less robust but cheap to buy so is popular in homes. Ink-jet is better at printing high-quality photographic images.
An impact printer physically strikes a ribbon and pushes it against the paper, thus leaving a trace. A dot matrix printer uses a matrix of pins that can be fired in different combinations against the ribbon to create different characters. A daisy wheel printer has a wheel of characters that rotates to the required character and then strikes the ribbon and paper underneath.
Impact printers are still used where carbon copy paper is used e.g. when orders are made and recorded.
Non-impact printers transfer ink to paper using electrostatics (a charge propels droplets of ink onto the paper) or dye sublimation (the ink goes directly from solid to gas). Print a line at a time (line printer) so the image builds up gradually as the paper advances. Inkjet printers produce high quality coloured output, good enough for photographers. Inkjet printers can be made in large formats e.g. 42 inches wide.
Basic inkjet printers use 4 colours, cyan, magenta, yellow and black (CMYK - the alternative colour model to RGB, which is for projection devices like screens and projectrors). More advanced models have additional inks to produce a greater range of colours or gamut e.g. 6 (light cyan, light magenta) or 8 (dark grey and light grey for monochrome output) or even 10 or 12.
The coloured inks are mixed and produce light of different colours, which is reflected back tio the eye. Blue is produced by mixing cyan and magenta. A mixture of CYM eliminates most light so appears black, but not enough for quality printing so there is a separate black ink cartridge.
For best quality special paper is used e.g. Hahnemuller - Redcliffe Imaging
Inkjet printers may be cheap to buy but expensive to run: Inkjets Dirty Secret
Inkjet printers are versatile and have a range of applications: Colaris
A laser printer prints a page at a time: page printer. A page description language e.g. Postscript describes a page in mathematical terms. A processor in the printer generates a bitmap image from this. A negative charge is applied to a photosensitive drum; lasers are directed at the points on the drum that repesent the bitmap to neutralise the charge. Toner particles have a negative charge and are attracted to the positive areas, thus producing an outline of the bitmap. The drum is passed over paper and then fused at high temperature so the toner does not smudge. The amount of toner applied can be varied by adjusting the voltage applied to the gap between toner cartridge and drum as the paper passes between them. The information about what charge to apply is derived from the bitmap image held in memory.
Specialised output device with pens for output of drawings such as architectural and engineering plans.
Advantages: clear drawings drawn with continuous lines, not raster graphics, large scale drawings (up to A0)
Disadvantages: large and expensive
Output voice and music.
Advantages: Can hear sounds!
Disadvantages: Can be too noisy.
Provide output in a control system such as a burglar alarm, a heating system, a greenhouse (open windows when too hot).
Advantages: useful in a range of situations
Disadvantages: none