Output Devices

Q.       Discuss how a printer works?

Ans.: Working principle of Laser printer: Laser printers are page printers that print one page at a time. Main components of a laser printer are a laser beam source, a multi-sided mirror, a photoconductive drum, and toner. To print a page of output, the printer focuses the laser beam on the electro statically charged drum by the spinning multi-sided mirror. The mirror focuses the laser beam on the surface of the drum in a manner to create the patterns of characters/images that the printer has to print on the page. Since the drum is photo conductive, print mechanism creates a difference in electric charge on those parts of the drum surface, which are exposed to the laser beam. As a result, the toner, composed of oppositely charged ink particles, sticks to the drum in the places where the laser beam has charged the drum’s surface. The printer then applies heat and pressure to fuse the toner permanently on the paper to generate the printed output. It then rotates the drum and cleans it with a rubber blade to remove the toner sticking to its surface to prepare the drum for next page printing.

Q.       What do you know by impact printers? Describe with examples.

Ans.: Impact Printers: An impact printer has mechanisms resembling those of a typewriter. It forms characters or images by striking a mechanism such as a print hammer or wheel against an inked ribbon, leaving an image on paper. Impact printers are dying out; however, you may still come in contact with a dot-matrix printer. A dot-matrix printer contains a print head of small pins that strike an inked ribbon, forming characters or images. Print heads are available with 9, 18, or 24 pins; the 24-pin head offers the best print quality. Dot-matrix printers permit a choice between output of draft quality; a coarser-looking 72 dots per inch vertically, which may be acceptable for drafts of papers and reports, and near-letter-quality, a crisper-looking 144 dots per inch vertically, which is more suitable for a finished product to be shown to other people.

                  Dot-matrix printers print about 40-300 characters per second (cps) and can print some graphics, although the reproduction quality is poor. Color ribbons are available for limited use of color. Dot-matrix printers are noisy, inexpensive, and they can print through multipart forms, creating several copies of a page at the same time, which nonimpact printers cannot do.

Q.       What do you know by no-impact printers? Describe with examples.

Ans.: Non-Impact Printers: Nonimpact printers, used almost everywhere now, are faster and quieter than impact printers because they have fewer moving parts. Nonimpact printers form characters and images without direct physical contact between the printing mechanism and the paper.

Two types of nonimpact printers often used with microcomputers are laser printers and ink-jet printers.

                  Ink-jet printer Like laser and dot-matrix printers, ink-jet printers also form images with little dots. Ink-jet printers spray small, electrically charged droplets of ink from four nozzles through holes in a matrix at high speed onto paper. Ink-jet printers can print in color and are quieter and much less expensive than a color laser printer. A variation on ink-jet technology is the bubble-jet printer, which use miniature heating elements to force specially formulated inks through print heads with 128 tiny nozzles. The multiple nozzles print fine images at high speeds. This technology is commonly used in portable printers.

Q.       What is monitor?

Ans.: Monitors: Monitors are the most popular soft-copy output devices used today. They display an output on a television like screen. Two basics types of monitors are cathode-ray-tube (CRT) and LCD (Liquid Crystal Display) flat-panel.

Q.       Describe about LCD monitor?

Ans.: LCD monitors: The liquid crystal display (LCD) uses a clear liquid chemical trapped in tiny pockets between two pieces of glass. Each pocket of liquid is covered both front and back by very thin wires. When a small amount of current is applied to both wires, a chemical reaction turns the liquid dark, thereby blocking light. The point of blocked light is the pixel.

            The principal advantages of LCD are:

·         Low power consumption.

·         Low cost.

·         Small size.

            The major disadvantages of LCDs are:

·         LCDs do not emit light; as a result, the image has very little contrast.

·         Screen is susceptible to glare, so the optimum viewing angle is narrow.

·         LCDs have less color capability.

·         Resolution is not as good as that of a CRT.

Q.       What is the meaning of VGA?

Ans.: VGA: Video Graphics Array (VGA) refers specifically to the display hardware first introduced with the IBM PS/2 line of computers in 1987, but through its widespread adoption has also come to mean an analog computer display standard, the 15-pin D-subminiature VGA connector or the 640×480 resolution itself.

Q.       What is the meaning of SVGA?

Ans.: SVGA: Super Video Graphics Array or Ultra Video Graphics Array, almost always abbreviated to Super VGA, Ultra VGA or just SVGA or UVGA is a broad term that covers a wide range of computer display standards.

Q.       What is the meaning of XGA?

Ans.: XGA: XGA, the Extended Graphics Array, is an IBM display standard introduced in 1990. Later it became the most common appellation of the 1024×768 pixels display resolution. It was not a new and improved replacement for Super VGA, but rather became one particular subset of the broad range of capabilities covered under the "Super VGA" umbrella.

Q.       What factors you should consider before buying a monitor for your organization?

Ans.: The following things are considered for buying a monitor:

            Size: CRT monitors are big; they take up desktop space and can be difficult to move. By contrast flat-panel monitors are gaining popularity because of their comparatively lightweight.

            Power: CRT monitor require a log of power to run; therefore they are not practical for use with notebook computer. Instead notebook computers use flat-panel monitors that are less than 1 inch thick and which can run on battery power, which is built into the computer.

            Light: One disadvantage of flat-panel monitors is that their images can be difficult to see in bright light, for this reason laptop computers used often look for shady place to sit when working outdoor or near windows. But CRT monitors has not this type of problem. Anywhere you work with CRT monitors.

            Viewing angle: A bigger disadvantages of flat-panel monitors however is their viewing angle that is the angle from which the display’s image can be viewed clearly. With most CRT monitors you can see the image clearly even when standing an angle to the screen. In flat-panel monitors, however the viewing shrinks as you increase your angle to the screen, the image becomes fuzzy quickly. In many older flat-panel systems, the user must face the screen nearly straight on to see the image clearly.

            Well, the first thing you need to determine when choosing a monitor is if you want to get a CRT Monitor or an LCD monitors. CRTs are the old big clunkers, cathode ray tubes. LCDs are the nice, flat panel liquid crystal displays. There are a lot fewer emissions on the LCDs so they’re easier on your eyes, as well as being better for the environment; they use less power. Then, of course, you want to look at the resolution that the monitor can support. With higher resolution, you’ll get a crisper image. It’ll be sharper with less strain on your eye. However, on the same not, you need to make sure that your computer can drive the resolution of your screen. Y You can buy really high end screen, which can be really high resolution, but your computer’s graphic card may not be able to output the resolution.

Q.       Discuss about monitor.    

Ans.: Monitor: A monitor or display (also called screen or visual display unit) is an electronic visual display for computers. The monitor comprises the display device, circuitry, and an enclosure. The display device in modern monitors is typically a thin film transistor liquid crystal display (TFT-LCD) thin panel, while older monitors use a cathode ray tube (CRT) about as deep as the screen size.

                          Originally, computer monitors were used for data processing while television receivers were used for entertainment. From the 1980s onwards, computers (and their monitors) have been used for both data processing and entertainment, while televisions have implemented some computer functionality. The common aspect ratio of televisions, and then computer monitors, has also changed from 4:3 to 16:9 (and 16:10).

Multiple technologies have been used for computer monitors. Until the 21st century most used cathode ray tubes but they have largely been superseded by LCD monitors.

           

            Cathode ray tube: The first computer monitors used cathode ray tubes (CRT). Until the early 1980s, they were known as video display terminals and were physically attached to the computer and keyboard. The monitors were monochrome, flickered and the image quality was poor.

           

            Liquid Crystal:       There are multiple technologies that have been used to implement Liquid Crystal Displays (LCD). Throughout the 1990s, the primary use of LCD technology as computer monitors was in laptops where the lower power consumption, lighter weight, and smaller physical size of LCDs justified the higher price versus a CRT.

Organic light-emitting diode: Organic light-emitting diode (OLED) monitors provide higher contrast and better viewing angles than LCDs, and are predicted to replace them. In 2011, a 25 inch OLED monitor costs $6000[citation needed], but the prices are expected to drop.

Measurements of performance: The performance of a monitor is measured by the following parameters: Luminance is measured in candelas per square meter (cd/m2 also called a Nit). Aspect, Viewable image size, Display resolution, Dot pitch, Refresh rate, Response time, Contrast ratio, Power consumption, Delta-E, Viewing angle.

Q.       What is meant by the terms resolution?

Ans.: Resolution: The term resolution refers to the sharpness or clarity of an image. A monitor’s resolution is determined by the number of pixels on the screen, expressed as a matrix. The more pixels a monitor can display, the higher its resolution and the clearer its images appear.

Q.       What is meant by the terms dot pitch?

Ans.: Dot Pitch: The last criti9cal specification of a color monitor is the dot pitch, the distance between the like-colored phosphor dots of an adjacent pixel. Dot pitch is measured as a fraction of a millimeter, and dot pitches can range from .15 mm to .40 mm or higher.

Q.       What is meant by the terms refresh rate?

Ans.: Refresh Rate: a monitor’s refresh rate is the number of times per second that the electron guns scan every pixel on the screen. Refresh rate is important because phosphor dots fade quickly after the electron fun charges them with electrons. If the screen is not refreshed often enough, it appears to flicker, and flicker is one of the main causes of eyestrain. Refresh rate is measured in Hertz (Hz), or in cycles per second.

Q.       What are the advantages and disadvantages of CRT and flat-panel display?

Ans.: Advantages and disadvantages of CRT and flat-panel display:

CRT monitors have been around since the invention of the personal computer. The newer flat panel computer monitors have a few advantages when compared to the older design. Some of these include power, radiation, and space. This article will discuss some of the advantages of flat panel computer monitors.

·         Power: One of the first advantages of flat panel computer monitors deals with power. These monitors consume much less power than CRT monitors. This will definitely benefit you if you frequently use your computer. You will save a lot of money on your energy bill by using flat      panel computer monitors.

·         Radiation: One of the next advantages of flat panel computer monitors deals with radiation. Traditional CRT monitors emit radiation that can be harmful over time if you spend a lot of time in front of your computer. Flat panel computer monitors have a lot fewer emissions than CRT monitors. Therefore, they are a lot safer to use.

·         Space: Most people buy flat panel computer monitors because they take up less space. CRT monitors are very bulky and can easily take up half of your desk. Flat panel computer monitors use their size efficiently, as they are usually just a few inches thick. This will allow you to use more of the space on top of your desk.

·         Size: One of the next advantages of flat panel computer monitors deals with their sizes. They are usually available in larger sizes than CRT monitors. They can come in wide screen or extra-large screen sizes. Since flat panel computer monitors are thinner, you can easily bit their larger sizes wherever you need to.

·         Environment: One of the final advantages of flat panel computer monitors deals with the environment. These monitors are much more environmentally friendly. CRT monitors have more parts to get rid of. They also need to be disposed on carefully as some of their contents can harm the environment. Flat panel computer monitors have fewer parts to get rid of. This      also means that LCD monitors will take up less space in the landfills.

These are some of the advantages of flat panel computer monitors. They consume a lot less power than traditional CRT monitors, so you would save money on your energy bill if you use your computer frequently. Also, flat panel computer monitors take up a lot less space on your desk because they are much thinner than CRT monitors.

Q.       Write down the working principle of a CRT monitor with diagram.

Ans.: Working principle of a CRT monitor: An electron beam produced at the cathode is accelerated and focused to strike on the screen. The screen is covered with phosphor dots which can emit light of specific colors when executed. The three kinks of phosphor used of the dots emit red, green or blue light respectively when struck by an electron beam. Red, green and blue are called the primary colors and by combining light of these three colors at the correct ratio, all other colors (composite colors) can be produced. To generate and image on the screen, the electron beam scans on the screen, the electron beam scans across the phosphor dots according to the information taken from the video signals. The phosphor dots at each position on the screen light up with the correct color and intensity to create the desired image.