Edexcel GCSE Computer Science (1CP2) Exam Questions

• A Amplitude (1)
• The only correct answer is A. The correct answer is amplitude (the height of the sound wave).
• B is not correct because bit depth is the number of bits used to store each sample
• C is not correct because sample interval is the time between samples
• D is not correct because sample rate is the number of samples taken each second

Award one mark for:

• 11 (characters) (1)

Allow 11 remainder 3.

Allow 80 ÷ 7 = 11.428... rounded down to 11.

Do not accept 11.4 or 12 (rounding up or giving a decimal answer).

Do not award an unevaluated calculation such as 80 ÷ 7 with no answer.

Award one mark for:

• The number of bits used per sample (1)

Allow bits per sample

Allow the number of bits used to record/store each sample

Do not accept the number of samples taken per second (sample rate)

Do not accept the number of bits used to store the whole sound file

Do not accept the number of levels/amplitude values a sample can take

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

• (Only) 128 different characters can be represented / 7 bits give 2^7 = 128 different codes (1)
• It cannot represent characters from languages other than English / non-English alphabets, e.g. Greek, Chinese (1)
• It cannot represent accented characters, e.g. é, ñ (1)
• It cannot represent symbols or emoji that are not in the ASCII character set (1)

Award a maximum of one mark for the last three bullets, as they are all examples of characters that fall outside the 128 ASCII codes.

Allow 'it can only represent 128 characters, so some characters are missing' for the first bullet.

Do not accept 'it uses 7 bits' / 'it only uses 7 bits' on its own, without saying what this limits.

Do not accept 'it can only store a limited amount of text' / 'it can only store short messages', as 7 bits limits the number of characters available, not the length of a message.

Do not accept 'it can only represent the characters in the ASCII character set', as this repeats the question.

Do not accept 'it is old/out of date' or 'it cannot store numbers'.

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 denary code 77 is converted to binary (1) to give the 7-bit pattern 1001101 (1)
• The character M is represented by a unique ASCII code/number (1) that is stored as a 7-bit binary pattern (1)
• 7 bits are used to store the code for M (1) so 128 different characters can be represented (1)
• The binary pattern 1001101 is stored in memory (1) using one 7-bit code for each character (1)

Do not accept answers that only state the ASCII code 77, as this is given in the question.

Do not accept 01001101, as this is an 8-bit pattern.

Do not accept ASCII described as a programming language or a method of encryption.

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

• Two bits give only four possible binary values (1) so at most four colours can be represented (1)
• Only 2^2 = 4 colours can be stored (1) so colours in the original image may be lost/changed (1)
• There are not enough bit patterns for more than four colours (1) so the image cannot show all the colours it needs (1)
• Each pixel has a limited set of codes (1) so similar colours may become the same colour (1)

Do not accept 'the image will be low resolution' or 'it will be poor quality' alone.

Do not award responses about file size.

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

• Only a fixed number of amplitude values/levels can be represented (1) so the amplitude is rounded to the nearest available value/level (1)
• Fewer amplitude values/levels are available to choose from (1) so similar/close amplitudes cannot be stored as different values (1)
• The exact amplitude often falls between available values/levels (1) so the stored amplitude is not exact/less accurate (1)

Answers must relate to the number of bits per sample (bit depth) and the amplitude values/levels it can represent.

Do not accept answers about the sample rate, sample interval or the number of samples taken, or that confuse bit depth with the number of samples.

Do not award 'lower quality'/'more detail'/'less detail' unless it is linked to the number of amplitude values/levels.

Do not accept 'the sound cannot be played/stored' without a linked limitation.

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

• More samples are taken every second / the sample rate is higher (1) so the digital wave follows the shape of the analogue wave more closely (1)
• The amplitude is measured more often / at shorter intervals (1) so fewer changes in the sound are missed between measurements (1)
• The sample interval is shorter (1) so less of the sound wave is lost/goes unrecorded between samples (1)
• More data points are recorded for the same length of sound (1) so the digital representation is a closer copy of the original sound (1)

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

Do not accept 'the quality is better/higher' or 'the sound is clearer' as a point on its own without a reason such as more samples or more detail.

Do not accept 'the samples are more accurate' or 'more data is collected' without saying what becomes more accurate or what the extra data records.

Do not accept 'the file size is larger' as a reason for improved quality.

Do not accept answers about using more bits per sample, as these describe bit depth, not the sample rate.

Indicative content

Pixels

• A bitmap image is made up of picture elements, called pixels.
• Each pixel is the smallest identifiable area of the image and has a single colour.
• The logo is stored as a grid of pixels, and its width and height in pixels give its dimensions.
• Each pixel is stored separately, so a larger grid needs more pixel values to be stored.

Binary values

• Each pixel's colour is represented by a binary value.
• The number of bits used for each pixel is the colour depth.
• With n bits per pixel there are 2^n different binary values, so 2^n possible colours.
• A black-and-white image can use one bit per pixel, with 0 for white and 1 for black.
• More bits per pixel allow more colours to be represented in the logo.

Grid

• The binary values are stored in order, row by row, so the computer can rebuild the grid.
• The resolution is the number of pixels in the image, for example width × height.
• A higher-resolution grid stores more pixels, so the logo can show more detail.
• The image file stores the pixel values and data such as the image dimensions.

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 pixels and binary values.

Do not accept resolution as the number of colours.