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Computer Science > 5. Input and output devices > Flashcards

5. Input and output devices Flashcards

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1
Q

How does a 2D scanner work?

A
  1. The document is placed on a glass panel and the cover is closed.
  2. A bright light illuminates the document.
  3. The scan head moves across the document to produce an image of the document which is sent to a lens using mirrors.
  4. The lens focuses the image onto a charge couple device formed of photoelectric cells which create electric charge when the light falls on them.
  5. Software produces a digital image from the electronic form.
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2
Q

What is OCR?

A

Optical character recognition - converts scanned image into a text file format.

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3
Q

What is OMR?

A

Optical mark recognition - can recognise if boxes are filled or not from a scanned image.

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4
Q

How are 2D scanners used at an airport?

A

OCR is used to fill a database with the details of a passenger. Scanners are also used to scan the photo and compare it to a photo taken of the passenger.

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5
Q

How does a 3D scanner work?

A

Takes several images at points along the x, y and z coordinates and compiles them into one computer generated 3D model.

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6
Q

What is an application of a 3D scanner?

A

CT scanners - used for medical diagnostics.

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7
Q

How does a barcode scanner work?

A

The barcode is scanned using an red LED or laser. Light is reflected off of the white areas and is read by sensors. The sensors build up a pattern of light and dark regions.

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8
Q

How are barcode scanners used in supermarkets?

A

When a barcode is scanned, a computer automatically looks up the product in the database and the price and other details are sent to the checkout. The number of items in stock is automatically decreased and if it falls below a certain level more stock is ordered.

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9
Q

How does a QR code work?

A

A QR code is a type of barcode that can be scanned by a mobile phone. The can contain text, links and adverts.

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10
Q

How does a digital camera work?

A

The camera is controlled by a microprocessor that can adjust the camera settings such as the shutter speed, focus, flash, aperture and size of the image. The photo is captured when light passes through the lens onto a light sensitive cell made up of pixels.

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11
Q

How does a keyboard work?

A

When each key is pressed it creates a different signal which is interpreted by the computer and translated in to ascii or unicode.

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12
Q

What is a problem with a conventional keyboard and how can it be solved?

A

Repetitive strain injury (RSI). Can be solved using an ergonomic keyboard which has the keys arranged differently and offers more support for the wrist.

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13
Q

What are the two ways that a conventional mouse can work?

A

With a mechanical ball or led.

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14
Q

What are the advantages of a trackerball?

A

Less risk of RSI and takes up less space.

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15
Q

How does a microphone work?

A

When the microphone picks up a sound a diaphragm vibrates producing an electric signal which is converted to digital data.

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16
Q

What is the difference between voice recognition and speech recognition?

A

Voice recognition confirms if the person is who they should be; speech recognition recognises individual words spoken.

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17
Q

How does voice recognition software work?

A

A few words spoken by the user are recorded and converted into a digital wave pattern. The software compares the pattern to a stored one to see if they match.

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18
Q

How does speech recognition software work?

A

The computer converts the wave pattern into digital form. The software breaks the data into phonemes (the smallest elements that make up a language e.g. ‘h’, ‘uh’, ‘t’). The phonemes are then compared to words found in the built in dictionary and the most likely match is returned.

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19
Q

What are the three(/four) types of touch screen?

A

Capacitive, infra-red (heat and optical) and resistive.

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20
Q

How does a capacitive touch screen work?

A

The screen is made up of lots of layers of glass that act like a capacitor. When the top layer is pressed the current changes and the coordinates where the screen was touched is determined by an on-board microprocessor.

21
Q

How does an infra-red touch screen work?

A

Heat sensitive - Detects a warm object.
Optical - Uses an array of sensors in the form of a grid and the coordinates of the area touched are determined by where on the grid the screen is touched.

22
Q

How does a resistive touch screen work?

A

Made of a top layer of polyester and a bottom layer of glass. When the top layer is pressed it touches the bottom and makes a circuit. Signals are then sent out which are interpreted by a microprocessor.

23
Q

What are the advantages and disadvantages of capacitive technologies?

A 
Advantages:
- Medium cost
- Good visibility in strong sunlight
- Permits multi touch
- Very durable
Disadvantages:
- Only works with bare fingers
24
Q

What are the advantages and disadvantages of infra-red technologies?

A 
Advantages:
- Permits multi touch
- Optical allows gloved fingers/sylus
- Both quite durable
Disadvantages:
- Relatively expensive
- Heat-sensitive only works with bare fingers
- Fairly good visibility in strong sunlight?
25
Q

What are the advantages and disadvantages of resistive technologies?

A 
Advantages:
- Relatively inexpensive
- Allows gloved fingers/stylus
Disadvantages:
- Poor visibility in strong sunlight
- Doesn't permit multi touch
- Fairly durable - gets scratched and wears out after a while.
26
Q

What is a temperature sensor used for?

A
  • Control central heating
  • Control/monitor a chemical process
  • Control/monitor a temperature in a greenhouse
27
Q

What is a moisture/humidity sensor used for?

A
  • Control/monitor the moisture levels in the soil in a greenhouse
  • Control/monitor the humidity in the air in a greenhouse
  • Dampness levels in an industrial application e.g moisture in a paint spray booth
28
Q

What is a light sensor used for?

A
  • Switch street lighting on/off
  • Control/monitor the light levels in a greenhouse
  • Switch car headlights on
29
Q

What is an infra-red/motion sensor used for?

A
  • Turn on car windscreen wipers automatically
  • Detect intruders in burglar alarm system
  • Count people entering/leaving building
30
Q

What is a pressure sensor used for?

A
  • Detect intruders in burglar alarm system
  • Weigh things
  • Control/monitor a chemical process where gas pressure is important
31
Q

What is an acoustic/sound sensor used for?

A
  • Detect intruders in burglar alarm system

- Detect the noise of a liquid dripping in a pipe

32
Q

What is a gas sensor used for?

A
  • Monitor pollution levels in water or the air
  • Control/monitor 02/CO2 levels in a greenhouse
  • Check for CO2 leaks in a powerstation
33
Q

What is a pH sensor used for?

A
  • Control/monitor pH of soil in a greenhouse
  • Monitor pollution in water
  • Cheese making
34
Q

What is a magnetic field sensor used for?

A
  • Anti-lock braking systems in cars
  • CD players
  • Mobile phones
35
Q

What is the difference between monitoring and controlling systems?

A

Monitoring systems have no effect on the situation, just report it to the user whereas control sensors adjust the settings e.g. turn light on if it’s dark.

36
Q

How do interactive whiteboards work?

A

Interactive whiteboards allow images to be projected on a board using a projector which can have text/images added to them and stored in a digital form.

37
Q

What do the printer driver and printer buffer do?

A
  1. The data is sent to the printer driver from the computer.
  2. The printer driver checks the data is in an appropriate format and that the printer is ready to print.
  3. The data is then stored in the printer buffer
    (4. Document is printed by laser or inkjet printer)
  4. If there is more data in the printer buffer it is printed.
  5. Once the buffer is empty an interrupt is sent to the computer.
38
Q

How does an inkjet printer work?

A
  1. A sheet of paper is fed into the main body of the printer. A sensor checks if there is more paper in the feed tray and that there are no jams.
  2. As the paper is fed into the printer the print head moves from side to side and sprays the four ink colours in the right combinations to create the exact colour.
  3. At the end of each pass of the print head the paper is moved on slightly until whole page is printed.
  4. If there is more data in the printer buffer the process is repeated.
39
Q

How does a laser printer work?

A
  1. The printing drum is given a positive charge.
  2. As the drum spins a laser marks out areas to be print leaving those areas negatively charged.
  3. The drum is coated with positively charged toner which sticks to the negative areas of the drum.
  4. A negatively charged sheet of paper is rolled over the drum and the toner sticks to it.
  5. The electric charge is removed from the printer.
  6. The paper goes through a fuser which melts the ink onto the page.
  7. A discharge lamp removes all the charge from the drum.
40
Q

Advantages of inkjet printers

A

Cheaper to buy
More compact
Ink cheaper than toner
Cheaper to have repaired

41
Q

Advantages of laser printers

A

Faster
Cheaper cost per page
Quiet
Toner doesn’t have to be replaced as often as ink

42
Q

What are the two ways that 3D printers work?

A

Direct 3D printers - printhead moves in x,y and z directions and builds up layers using material.
Binder 3D printers - uses two passes of the printhead for each layer - the first sprays down dry powder and the second sprays a binder (type of glue) to form a solid layer.

43
Q

What are the advantages of LED monitors compared to CCFL monitors?

A 
Reach maximum brightness almost immediately
Whiter light
Brighter 
Last longer
More energy efficient
44
Q

How do LCD monitors work?

A

The front of the screen is made up of groups of red, green and blue liquid crystal diodes. The screen is backlit using either CCFL or LEDs.

45
Q

What is an OLED?

A

Organic light emitting diode - uses organic chemicals to create semi-conductors which, when an electric field is applied to them, give off light.

46
Q

What are the advantages of OLED?

A

Thinner
More flexible
Brighter than LEDs
Don’t require backlighting - use less power
Can be made into large sheets for advertising
Large field of view

47
Q

What are the two types of projectors?

A

Digital light and LCD

48
Q

How do digital light projectors work?

A

Uses millions of micro mirrors on a DLP chip which can be on or off depending on whether they tilt towards the light source. They can tilt back and forth thousands of times per second creating different shades of grey. Light from a xenon bulb passes through a colour filter on it’s way to the chip which splits it into the primary colours. It then passes through the DLP chip which creates the image in over 16 million colours.

49
Q

How do LCD projectors work?

A

A powerful beam of white light is sent to a group of chromatic coated mirrors which reflect the light back at the wavelengths of the primary colours. The different colours then each pass through a different LCD screen which shows the image in grey scale. A prism combines the light into a single image which then passes through a lens onto a screen.

Computer Science (10 decks)

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