GCSEComputer ScienceEdexcelExam Questions2. DataData Representation

Data Representation (Edexcel GCSE Computer Science): Exam Questions

Exam code: 1CP2

16 mins3 questions
1a
2 marks

The ASCII system is used to represent letters and symbols.

(i) State the number of bits used to represent each letter or symbol in ASCII.

[1]

(ii) The ASCII code 65 represents the letter A.

Give the letter represented by the ASCII code 68.

[2]

How did you do?

1b
1 mark

Sound waves are converted to binary using sample intervals.

Define the term ‘sample interval’.

How did you do?

1c
2 marks

Give an expression to calculate the size of a bitmap image, not the size of the file that stores the image.

How did you do?

2a
2 marks

Here is an original image.

Optical illusion with two dark diagonal bars on grey, crossed by vertical black and white squares, creating a zigzag pattern effect.

There is one bit available to represent each pixel.

Explain one reason why the image cannot be accurately represented using one bit for each pixel.

How did you do?

2b
6 marks

An analogue sound is represented in digital form.

The sound is one second long and is sampled at 10Hz.

The digital representation has a bit depth of 5 and is stored in two’s complement.

Sound data:

0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1

Draw a graph to represent the data sampled.

You must include:

  • labels for the x and y axes

  • values for the x and y axes

  • each sample plotted as an cross times

  • samples joined up to show the digital form.

A grid with intersecting bold lines, forming a right angle, stretches horizontally and vertically across the graph paper.

How did you do?

3a
2 marks

Data can be encoded using ASCII.

Describe ASCII.

How did you do?

3b
1 mark

A pixel is the smallest element in a bitmap image.

Two images are displayed on the same screen.

One image is 1280cross times720 pixels. The second image is 1920cross times1080 pixels.
The second image has a higher resolution.

State one reason why the second image will be displayed in more detail.

How did you do?