Edexcel GCSE Computer Science (1CP2) Exam Questions

• B 7 (1)
• The only correct answer is B. The correct answer is 7.
• A is not correct because 6 bits give only 64 combinations, which is not enough for 70 characters
• C is not correct because 7 bits already give 128 combinations, so 8 bits is not the minimum needed
• D is not correct because 70 is the number of characters needed, not a number of bits

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

• Only a limited/fixed number of amplitude values can be stored (1)
• The amplitude of each sample is rounded/approximated to the nearest value that can be stored (1)
• The recording is less accurate than the original analogue sound/does not match the analogue wave exactly (1)
• Sounds louder than the highest amplitude that can be stored are clipped/distorted (1)
• Sounds quieter than the lowest amplitude that can be stored cannot be represented/are lost (1)

Allow quantisation error/noise for the amplitude being rounded to the nearest value that can be stored, but do not award a second mark for the same idea

Allow a stated consequence as a separate mark only when it is a different point from the list, e.g. fewer amplitude values can be stored (1) so very quiet sounds are lost (1)

Do not accept 'lower quality'/'poorer sound' on its own; the answer must say the recording is less accurate than the original/does not match the analogue wave

Do not accept sample rate/sample interval/number of channels (stereo/mono), as these are not limited by the number of bits available for each sample

Do not accept remedies such as 'a larger bit depth would make it more accurate', as these do not describe a limitation

Do not accept answers about file size, compression or playback method

Do not accept a statement that repeats the stem, e.g. 'the sound is stored in binary using a fixed number of bits'

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:

• Each pixel is stored as a binary value/code (1) which represents/maps to a colour (1)
• The binary value is used to look up a colour in a palette (1) so the pixel can be displayed in that colour (1)
• A bit pattern is assigned to each colour (1) and each pixel stores the bit pattern for its colour (1)
• The number of bits per pixel sets how many different colour codes exist (1) so each code can represent a different colour (1)

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

Do not accept 'pixels are binary' or 'the image is made of 1s and 0s' without saying a pixel's colour is represented by a binary value.

Do not accept RGB values stored as denary or hexadecimal.

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'.

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

• Each sample is stored using more bits (1) so the amplitude can be recorded more precisely (1)
• More different amplitude values can be represented (1) because each extra bit doubles the number of possible values (1)
• The height of the wave at each sample point is measured more accurately (1) so the digital wave is closer to the analogue wave (1)
• The gap between the true amplitude and the stored value is smaller (1) because there are more values for the sample to be rounded to (1)

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

Do not accept 'the sound is sampled more often' or 'more samples are taken per second', as these describe the sample rate, not the bit depth.

Do not accept 'the file size increases' on its own as an effect on the representation of the sound.