← IGCSE Computer Science Paper 1

Optical mouse

An input device with an LED or laser under it that lights the surface while a sensor takes rapid images to track movement and move the pointer. It has no ball.

Part of: IGCSE Computer Science 0478 — 3.2 Input and Output Devices — Module 4, IGCSE Computer Science 0478 — 4.1 Types of Software and Interrupts — Module 48

Understanding Optical mouse in IGCSE Computer Science Paper 1

What it does: The LED or laser light shines on the desk surface, which lets the sensor take clear images of it. Older mice used a rolling ball to detect movement, whereas an optical mouse uses light and an image sensor, so it has no ball. The mouse is an input device. It sends the movement data to the computer, and the computer moves the pointer. The buttons and scroll wheel send clicks and scrolling to the computer. The LED only lights the surface.

Common mistakes: An optical mouse needs rapid images of the surface so it can see how the pattern changes as it moves. One image cannot show movement. It should say 'sensor takes rapid images'. An optical mouse has no ball. It sends the movement (distance and direction) worked out from the images. It should say 'send movement to the computer'.

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This module's key terms are also in a printable crossword (Modules 240–251) and word search (Modules 240–261).

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Learning
Duo
How does an optical mouse detect movement?
A sensor takes rapid pictures of the surface and compares themA rubber ball rolls and turns two rollers inside the mouse
Matches
An optical mouse tracks movement using a rolling ball under it
↓
This describes an older ball mouse. An optical mouse has no ball and uses an LED or laser and an image sensor instead.
Applying
Meanings
Term
optical mouse
Meaning
An input device with an LED or laser under it that lights the surface while a sensor takes rapid images to track movement and move the pointer. It has no ball.
Practice
REPEAT
Testing
Gaps
led ←
Check Answer
Spots
1LED lights the surface
2sensor takes one image only

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Quick Questions

1. How does an optical mouse detect movement?
A. A sensor takes rapid pictures of the surface and compares them ✓
B. A rubber ball rolls and turns two rollers inside the mouse
An optical mouse tracks the changing images of the surface. A rolling ball was used in older mechanical mice.
2. Which light source is found under an optical mouse?
A. A light bulb
B. An LED or laser ✓
Optical mice use a small LED or laser to light up the surface so the sensor can see it clearly.
3. True or false: an optical mouse has a moving ball underneath.
A. True - the ball turns as the mouse moves
B. False - it has no ball ✓
Optical mice have no moving ball. Older mechanical mice used a ball, which is why they got dirty and needed cleaning.
4. What does the image sensor in an optical mouse do?
A. Takes many images of the surface every second to work out distance and direction ✓
B. Records the user's voice to work out where to move the pointer
The sensor compares each image with the last one to see how far and in which direction the mouse has moved.
5. What happens to the movement data the mouse works out?
A. It is sent to the computer, which moves the pointer on the screen ✓
B. It is printed out as a document
The mouse is an input device. It sends the movement data to the computer, and the computer moves the pointer.

Match the Pairs

optical mouse → An input device that lights the surface with an LED or laser and uses a sensor to track movement
image sensor → A tiny camera chip that takes rapid pictures of the surface so changes in the image show the mouse movement
The mouse lights the surface under it with an LED or laser so the sensor can see the surface clearly → LED or laser light
Unlike older mice, an optical mouse has no moving ball inside it to track movement → no ball
An optical mouse tracks movement using a rolling ball under it → This describes an older ball mouse. An optical mouse has no ball and uses an LED or laser and an image sensor instead.
The scroll wheel and buttons on an optical mouse track the movement of the mouse → The buttons and scroll wheel send clicks and scrolling to the computer. The image sensor tracks the movement.

Key Term

optical mouse
An input device with an LED or laser under it that lights the surface while a sensor takes rapid images to track movement and move the pointer. It has no ball.

Fill in the Blanks

1. led ← ON
Hint: Type the state that makes the LED light up the surface under the mouse.
2. image ← CAPTURE(sensor)
Hint: Type the command name that makes the image sensor take a picture of the surface.
3. dx ← newX - oldX
Hint: Type the operator that works out how far the mouse has moved by finding the difference between two positions.
4. IF leftButton = PRESSED THEN SEND("click") ENDIF
Hint: Type the keyword that follows the condition and begins the code that runs when the button is pressed.
5. SEND(dx, dy) TO computer MOVE(pointer, dx, dy)
Hint: Type the command name that shifts the on-screen pointer using the movement data sent to the computer.

Spot the Error

Question 1
A LED lights the surface
B sensor takes one image only
C compare image with last image
D send movement to computer
Line B — An optical mouse needs rapid images of the surface so it can see how the pattern changes as it moves. One image cannot show movement. It should say 'sensor takes rapid images'.
Question 2
A LED shines light on the desk
B sensor captures images
C compare with previous image
D send ball turns to computer
E computer moves the pointer
Line D — An optical mouse has no ball. It sends the movement (distance and direction) worked out from the images. It should say 'send movement to the computer'.
Question 3
A ball rolls on the surface
B sensor takes rapid pictures
C movement sent to computer
D pointer moves on screen
Line A — An optical mouse uses an LED or laser to light the surface. It does not use a rolling ball, which belongs to older mice. It should say 'LED shines light under mouse'.
Question 4
A user presses left button
B mouse sends no signal
C computer selects the item
Line B — Pressing a button makes the mouse send a click signal to the computer. If no signal were sent, nothing could be selected. It should say 'mouse sends a click signal'.
Question 5
A user turns the scroll wheel
B mouse detects the turn
C mouse sends scroll signal
D the pointer changes colour
Line D — A scroll wheel signal makes the page move up or down. It does not change the pointer colour. It should say 'page moves up or down'.

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