4.7.4.1 Input and output devices

Question 1

How does a laser printer work?

Answer 1

The print drum is covered in a negative static charge. The laser beam is shone onto the drum using a rotating mirror. The laser is modulated (turned on and off) to remove the electric charge on the drum where the image should be black. The toner is given a negative charge and is transferred from drum to the paper and fused to the paper using heated rollers.

Question 2

How does a barcode reader work?

Answer 2

A laser is shone at the barcode and moved across it, and light is reflected back. The black bands reflect less light than the white ones and a light sensor measures the amount of light. The reflected light is converted into an electric signal which are passed through an equation to calculate a check digit. If the check digit on the barcode matches the result the barcode is accepted.

Question 3

How does a digital camera work?

Answer 3

The lens focuses light onto the image sensor, a CMOS device. The CMOS sensor uses many transistors to generate binary values from the light. When the shutter is pressed the image is captured. A colour filter is used to apply RGB colour components and the image is recorded as an array of pixels stored onto a solid state disk.

Question 4

How does RFID work?

Answer 4

The reader sends radio frequency waves to the antenna of the RFID tag, which energises it. The transponder in the tag sends the data signal and the reader receives it. This is used to track down stolen or lost items, track goods or identify things.

Question 5

What is the use of USB sticks?

Answer 5

It’s a small portable device that is easily written to and read from. More appropriate for smaller files. Robust device as no additional hardware is needed for it to work

Question 6

What is the use of magnetic tape?

Answer 6

It can hold large amounts of data and is used for slower access to files. Portable and has a fast data transfer rate.

Question 7

How does check digit work (in barcodes, etc.)?

Answer 7

The (12) data digits are passed through a function to calculate a check digit;
The result is compared against the check digit read in
If they do not match an error is indicated;
If they match the barcode is accepted and
processed;