Edexcel GCSE Computer Science (1CP2) Exam Questions

Award up to two marks for a linked explanation such as:

• Version B has more pixels in the same area (1) so each pixel represents a smaller part of the image (1)
• Version B has a higher pixel density (1) so finer detail can be represented (1)
• The pixels in Version B are smaller (1) so more detail can be captured in the same space (1)
• Version B has a higher resolution (1) because there are more pixels per unit of area (1)

For both marks, the expansion must follow/associate with the statement.

Do not accept 'more pixels' on its own without saying same area/pixel density/smaller pixels.

Do not accept higher colour depth or more colours.

Award up to two marks for a linked explanation such as:

• The computer looks up the character in the ASCII character set/table (1) to find the code that represents it (1)
• Each character has its own unique ASCII code (1) so the letter A is converted to and stored as a 7-bit binary pattern (1)
• ASCII uses 7 bits for each character (1) so A is stored as its ASCII code 1000001 (binary) / 65 (denary) (1)

The second mark requires a linked expansion, so a point on its own (e.g. 'A has the code 65') can only earn one mark.

For both marks, the expansion must follow/associate with the statement.

Accept an 8-bit pattern with a leading 0 (e.g. 01000001) as the binary code for A.

Do not accept 'the character is stored as text' without saying it is changed into a code/binary.

Do not accept a binary value on its own (e.g. 1000001) without saying that it is the ASCII code/that the character is converted to it.

Indicative content

Storing amplitude

• Each sample records the amplitude of the sound wave at that moment, and the amplitude is stored as a binary number.
• The bit depth is the number of bits used to store each sample, so it sets how many different amplitude values can be represented.
• With a bit depth of 8, there are 2^8 = 256 possible values for the height of the wave.
• The binary value for each sample tells the computer how loud the speech is at that point.

Accuracy

• A higher bit depth gives more possible values, so the recorded amplitude can be closer to the true amplitude of the speech.
• With a low bit depth, the amplitude must be rounded to the nearest available value, which adds quantisation error and makes the speech sound rough.
• A higher bit depth reduces the difference between the original wave and the digital version.
• Quiet parts of the speech may be lost or inaccurately recorded if the bit depth is too low.

File size

• A higher bit depth uses more bits for every sample, so the voice memo file is larger.
• A lower bit depth reduces the number of bits per sample, so the file is smaller and uses less storage on the phone.
• The developer must balance clear speech against storage space and download time.

Levels

• Level 0 (0 marks): No rewardable content.
• Level 1 (1–2 marks): Basic, independent points are made, showing elements of understanding of key concepts/principles of computer science. (AO1) The discussion will contain basic information with little linkage between points made or application to the context. (AO2)
• Level 2 (3–4 marks): Demonstrates adequate understanding of key concepts/principles of computer science. (AO1) The discussion shows some linkages and lines of reasoning with some structure and application to the context. (AO2)
• Level 3 (5–6 marks): Demonstrates comprehensive understanding of key concepts/principles of computer science to support the discussion being presented. (AO1) The discussion is well developed, with sustained lines of reasoning that are coherent and logically structured, and which clearly apply to the context. (AO2)

Level 3 responses must link the bit depth to both the accuracy of the amplitude and the file size.

Do not accept bit depth defined as the number of samples taken per second.