← IGCSE Computer Science Paper 1

LCD projector

An output device: a bright lamp shines light through red, green and blue LCD panels that form the image, then a lens focuses the recombined light onto a screen.

Part of: IGCSE Computer Science 0478 — 3.2 Input and Output Devices — Module 22

Understanding LCD projector in IGCSE Computer Science Paper 1

What it does: After passing through the three panels, the coloured light is combined into one beam. The lens then focuses that beam onto the screen. Classrooms and offices are typical uses because the projector enlarges an image so many people can see it at once. An LCD projector uses a bright lamp. Tiny moving mirrors belong to a DLP projector, not an LCD projector. A projector receives data from the computer and displays it for people to see, so it is an output device. LCD projectors are used in classrooms and offices to show images to a large group. A barcode scanner is used at a checkout.

Common mistakes: An LCD projector makes the image with LCD panels, not mirrors (mirrors are used in a DLP projector). It should be image = panels.filter(light). The LCD panels are for red, green and blue light. Yellow is not one of the three panels. It should be [red, green, blue].

Class: _____________________  ·  Name: _____________________  ·  Date: _________

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Learning
Duo
Which part of an LCD projector makes the image that is shown on the screen?
Small LCD panels that the light passes throughA laser that draws the picture on the screen
Matches
LCD projector: no lamp needed, the LCD panels make their own light
↓
LCD panels do not make their own light. An LCD projector needs a bright lamp (light source) to shine light through the panels.
Applying
Meanings
Term
LCD projector
Meaning
An output device: a bright lamp shines light through red, green and blue LCD panels that form the image, then a lens focuses the recombined light onto a screen.
Practice
1 Bright lamp shines white light
Testing
Gaps
An LCD projector is an device
Check Answer
Spots
2light = lamp.shine()
3image = mirrors.filter(light)

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Quick Questions

1. Which part of an LCD projector makes the image that is shown on the screen?
A. A laser that draws the picture on the screen
B. Small LCD panels that the light passes through ✓
The bright light passes through the LCD panels, and the panels form the image. The lens then focuses that light onto the screen.
2. What is the light source in an LCD projector?
A. A bright lamp ✓
B. Millions of tiny moving mirrors
An LCD projector uses a bright lamp. Tiny moving mirrors belong to a DLP projector, not an LCD projector.
3. How many LCD panels does an LCD projector use to build a colour image?
A. Three: one each for red, green and blue ✓
B. One panel for all the colours at once
There are separate LCD panels for red, green and blue light. The three coloured images are then combined.
4. What happens to the red, green and blue light after it passes through the LCD panels?
A. Each colour is sent to a separate screen
B. It is recombined into one image ✓
The three coloured beams are recombined into one full-colour image before they reach the lens.
5. What is the job of the lens in an LCD projector?
A. To focus the light onto the screen ✓
B. To produce the light for the image
The lamp produces the light. The lens only focuses the recombined light so the image is sharp on the screen.

Match the Pairs

LCD projector → An output device that shines a bright lamp through small LCD panels to make an image, then focuses it onto a screen with a lens
Red, green and blue LCD panels → Three small panels that each let through only some of the lamp's light to form one colour part of the image
The light is recombined and a lens focuses it so the picture is sharp on the screen → lamp -> RGB LCD panels -> recombine -> lens -> screen
An LCD projector is often used in a classroom so a teacher can show slides to a whole class → output_device = "LCD projector"; use = "classroom"
LCD projector: no lamp needed, the LCD panels make their own light → LCD panels do not make their own light. An LCD projector needs a bright lamp (light source) to shine light through the panels.
LCD projector: a lens splits the light into red, green and blue → The red, green and blue LCD panels form the colour parts of the image. The lens focuses the recombined light onto the screen. It does not split it.

Key Term

LCD projector
An output device: a bright lamp shines light through red, green and blue LCD panels that form the image, then a lens focuses the recombined light onto a screen.

Fill in the Blanks

1. An LCD projector is an output device
Hint: Type the kind of device that shows information to the user, rather than sending it in.
2. A bright lamp is the light source
Hint: Type the part that produces the strong light at the start of the process.
3. LCD panels: red, green and blue
Hint: Type the third colour that has its own LCD panel.
4. A lens focuses the light onto a screen
Hint: Type the part that focuses the recombined light.
5. Used in classrooms and offices
Hint: Type the workplace, besides classrooms, where projectors show presentations.

Spot the Error

Question 1
A lamp.switch_on()
B light = lamp.shine()
C image = mirrors.filter(light)
D lens.focus(image)
Line C — An LCD projector makes the image with LCD panels, not mirrors (mirrors are used in a DLP projector). It should be image = panels.filter(light).
Question 2
A lamp = bright_light()
B panels = [red, yellow, blue]
C light = recombine(panels)
D lens.focus(light, screen)
Line B — The LCD panels are for red, green and blue light. Yellow is not one of the three panels. It should be [red, green, blue].
Question 3
A lamp = dim_light()
B panels = [red, green, blue]
C image = form(lamp, panels)
Line A — An LCD projector needs a bright lamp so the image can be seen on a screen in a lit room. It should be lamp = bright_light().
Question 4
A projector = LCDProjector()
B projector.connect(laptop)
C projector.lamp.focus(screen)
D projector.show(slides)
Line C — The lens focuses the light onto the screen. The lamp only produces the bright light. It should be projector.lens.focus(screen).
Question 5
A light = lamp.shine()
B image = panels.form(light)
C beam = split(image)
D lens.focus(beam, screen)
Line C — After the red, green and blue panels form the image, the light is recombined into one beam, not split again. It should be beam = recombine(image).

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