Edexcel GCSE Computer Science (1CP2) Exam Questions

• C 128 (1)
• The only correct answer is C. The correct answer is 128.
• A is not correct because 6 bits give only 64 different combinations
• B is not correct because 127 is the largest 7-bit value, not the number of characters that 7 bits can represent
• D is not correct because 256 characters need 8 bits, as used by 8-bit extended ASCII

Award one mark for:

• The number of samples taken per second (1)

Allow captured/recorded for taken.

Allow 'samples per second'.

Allow 'each second' for 'per second'.

Allow Hz/hertz as the unit.

Do not accept the time between samples/sample interval.

Do not accept 'the number of samples' without a per second/time reference.

Do not accept the number of bits used per sample/bit depth.

Award one mark for any of the following:

• Increase the sample rate / take more samples per second (1)
• Increase the bit depth/sample resolution / use more bits per sample (1)
• Decrease the sample interval (1)

Do not accept increase the amplitude/volume

Do not accept decrease the sample rate / increase the sample interval

Award one mark for any of the following up to a maximum of two marks:

• The smallest element/area of a bitmap image (1)
• The smallest identifiable part of an image (1)
• Stores/represents a single colour as a binary value (1)
• Stores/represents a single colour using a number of bits/colour depth (1)

Allow 'picture element' for element/part in the first two bullets, but not on its own

Allow 'bit depth' for colour depth

Do not accept 'picture element'/'pixel' on its own

Do not accept 'a group of pixels' or 'a dot' on its own; allow 'dot' only when it is described as the smallest element/area of the image

Do not accept 'single colour' on its own for the second mark; it must be linked to a binary value/number of bits

Do not accept 'lots of coloured dots' (it contradicts a single colour)

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

• The bit depth is the number of bits used to store each sample/measurement (1) so a higher bit depth gives more possible/discrete values for the amplitude (1)
• A higher bit depth records the amplitude more accurately (1) because the stored value can be closer to the actual height of the wave (1)
• A low bit depth gives fewer possible amplitude values (1) so the amplitude is rounded to the nearest value, making the recording less accurate (1)

Do not accept sample rate/sample interval (number of samples per second) in place of bit depth.

Do not accept 'more bits gives better quality' or 'more accurate' on its own, without a development linked to the number of values or the amplitude stored.

Do not accept file size on its own, and a file size point cannot earn the second mark, as it does not describe the stored value.

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.

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:

• Only 4 colours can be represented (1) because 2 bits give 2^2 = 4 possible values (1)
• Some of the 12 colours cannot be stored (1) so they are lost/replaced with a colour that can be represented (1)
• The image will not match the original exactly (1) because there are fewer colour codes than the number of colours needed (1)
• Many colours will share the same binary value (1) so the image will lose colour detail (1)

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

Allow 'four colours' or '2^2'.

Do not accept 'only two colours' (confusing the number of bits with the number of values) or 'resolution is too low'.

Indicative content

What resolution means

• Resolution is the number of pixels in the image, or the number of pixels per inch.
• A photograph that is 6000 × 4000 pixels has a higher resolution than one that is 600 × 400 pixels.
• Resolution is not the same as colour depth or the number of colours.

Effect on detail

• A higher-resolution photograph has more pixels in the same area, so it can show more detail.
• A low-resolution photograph printed across a full page will look blocky or pixelated because each pixel is enlarged.
• A small website thumbnail uses fewer pixels on screen, so a lower-resolution version may still look sharp.
• A high-resolution original can be cropped and still contain enough pixels for a full-page print.

Effect on file size

• More pixels means more binary values must be stored, so the file is larger.
• A large file takes more storage and is slower to upload or download, which matters for visitors to the website.
• The photographer could make a lower-resolution copy for the website and keep the high-resolution original for print.
• File size also depends on the colour depth and the file format or compression used.

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 cover both detail and file size.

Do not accept resolution as the number of colours.