Edexcel GCSE Computer Science (1CP2) Exam Questions

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 codes run in alphabetical order/consecutively (1) so each letter has a code one more than the letter before it (1)
• A has the code 65 and Z has the code 90 (1) so the codes for the letters in between increase by 1 each time (1)
• The letters are stored in sequence (1) so B is A + 1, C is B + 1 and so on (1)

Accept the codes given in denary (65, 90) or as 7-bit binary (1000001, 1011010).

Do not accept 'the codes go up' or 'the codes are in order' on its own, as neither gives the step of 1 or links one letter to the next.

Do not accept 'each uppercase letter has a different code' on its own, as this does not describe the arrangement.

Indicative content

Sample rate and sample interval

• The sample rate is the number of samples taken each second, measured in hertz (Hz).
• The sample interval is the time between one sample and the next.
• The sample interval is the reciprocal of the sample rate, so doubling the sample rate halves the sample interval.
• A higher sample rate therefore gives a shorter sample interval, so the concert is measured more often.
• A lower sample rate gives a longer sample interval, so fewer points on the sound wave are recorded.
• The school could sample at 44,100 Hz, taking 44,100 measurements of the concert every second.

Accuracy of the recording

• A higher sample rate, and so a shorter sample interval, records more points on the sound wave, so its shape is followed more closely and the recording is more like the live performance.
• A higher sample rate can capture high-frequency sounds in the music, such as a violin, more accurately.
• With a low sample rate the gap between samples is long, so fast changes such as a drum beat can happen between samples and be missed, making the recording less accurate.
• If the sample rate is too low, a high-frequency sound changes several times between samples, so the digital file does not represent that sound properly.

Effect on file size

• Each sample is stored using a number of bits, so more samples each second means more data to store for each second of the concert.
• The file size is the sample rate multiplied by the bit depth multiplied by the duration, so doubling the sample rate doubles the size of the file for the same concert.
• A lower sample rate means fewer samples are stored, so the file is smaller and quicker to download from the school website.
• A higher sample rate gives a more accurate recording but a larger file, so the school must trade off quality against file size.

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)

Additional guidance

• Level 3 responses must cover both sample rate and sample interval, including how they are related, and link them to the accuracy of the recording and to the file size. For Level 2, the response must link a change in sample rate/sample interval to the accuracy of the recording and link a change to the size of the file, with some application to the concert; definitions alone, or points that are not linked, are Level 1.
• Accept reasoning that uses sample rate only, or sample interval only, if the relationship between them is stated or implied. Do not accept sample rate described as the number of bits per sample (that is bit depth), and do not accept the claim that a higher sample rate makes the file smaller.