Edexcel GCSE Computer Science (1CP2) exam questions

Build a practice paper from 514 exam-style questions, each with its mark scheme and example answers. Print it, or answer it on paper and then open the mark schemes. Or browse the questions by topic.

Practice paper

8 questions · 17 marks

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1Multiple choice1 markCharacter Sets Swap Remove

Characters are encoded using 7-bit ASCII.

Identify the number of different characters that can be represented using 7-bit ASCII.

[1 mark]

A64
B127
C128
D256

Mark scheme

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

Example answers and how they were marked

Full marks1/1

C 128

Why: Selects the only correct option (1): 7 bits give 2 to the power of 7, which is 128 different characters.

No marks0/1

D 256

Why: Near miss scoring 0: 256 is the number of characters that 8 bits give in extended ASCII, not 7-bit ASCII.

No marks0/1

B 127

Why: Misconception scoring 0, the off-by-one error the examiners' report describes: 127 is the largest 7-bit value, but 7 bits give 128 different characters.

2Short recall1 markSound Swap Remove

To store sound in binary, an analogue sound wave is sampled at regular intervals.

Define the term 'sample rate'.

[1 mark]

Mark scheme

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.

Example answers and how they were marked

Full marks1/1

The number of samples taken per second.

Why: States samples per second (1); 'per second' is accepted.

No marks0/1

The time between each sample.

Why: Defines sample interval, not sample rate; do not accept.

No marks0/1

The number of bits used for each sample.

Why: Describes bit depth, not sample rate; do not accept.

3Short recall1 markSound Swap Remove

A digital sound representation is created by sampling an analogue sound wave.

State one way the accuracy of this representation can be increased.

[1 mark]

Mark scheme

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

Example answers and how they were marked

Full marks1/1

Increase the sample rate.

Why: Creditworthy point: increase the sample rate (1).

No marks0/1

Decrease the sample rate.

Why: Near-miss: decreasing the sample rate reduces accuracy, so no mark; the mark scheme's do-not-accept line covers this (0).

No marks0/1

Increase the volume of the sound.

Why: Misconception: loudness/amplitude is not a way to increase sampling accuracy; do not accept increase amplitude/volume (0).

4Short recall2 marksImages Swap Remove

Bitmap images are stored as a grid of pixels.

Define the term pixel.

[2 marks]

Mark scheme

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)

Example answers and how they were marked

Full marks2/2

The smallest identifiable area of a bitmap image, which has one colour stored as a binary value.

Why: Smallest identifiable area (1) and single colour stored as a binary value (1)

Some marks1/2

The smallest part of a bitmap image, made of one colour.

Why: Smallest part (1); no credit for the second mark because the single colour is not linked to a binary value or number of bits

No marks0/2

A picture element made from lots of coloured dots.

Why: 'Picture element' on its own is not accepted and 'lots of coloured dots' contradicts a single colour

5Explain2 marksImages Swap Remove

A bitmap image uses a colour depth of 8 bits. Each pixel is stored as a binary value.

Explain how the colour of a pixel is represented in a bitmap image.

[2 marks]

Mark scheme

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.

Example answers and how they were marked

Full marks2/2

Each pixel stores a binary value (1); this value is used to look up the pixel's colour in a palette (1).

Why: Linked point (1) and reason (1): a binary value is stored for each pixel and maps to a colour.

Some marks1/2

A bit pattern is assigned to each colour.

Why: One mark for stating that colours have bit patterns; it does not say that each pixel stores the pattern for its colour.

No marks0/2

Each pixel stores the RGB colour as denary numbers between 0 and 255.

Why: Bitmap pixels are stored in binary, not as denary values; this common misconception earns no mark.

6Explain2 marksImages Swap Remove

An image uses a colour depth of 2 bits per pixel. The original image contains 12 different colours.

Explain why the image cannot be represented accurately at this colour depth.

[2 marks]

Mark scheme

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'.

Example answers and how they were marked

Full marks2/2

Only four colours can be represented (1) because two bits give four possible binary values (1).

Why: Linked point (1) and reason (1): 2 bits give 2^2 = 4 colour codes.

Some marks1/2

Only four colours can be represented.

Why: One mark for identifying that four colours can be represented; the linked reason about two bits giving four values is missing.

No marks0/2

Only two colours can be represented because each pixel has two bits.

Why: A common misconception: two bits give four possible values, not two, so no creditworthy point is given.

7Explain2 marksSound Swap Remove

Each sample of a sound wave is stored as a binary number.

Explain how increasing the bit depth affects the representation of a sound wave.

[2 marks]

Mark scheme

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.

Example answers and how they were marked

Full marks2/2

Each sample is stored using more bits, so the amplitude at each sample point can be recorded more precisely.

Why: Point (more bits per sample) (1) with linked reason (amplitude recorded more precisely) (1).

Some marks1/2

Each sample is stored using more bits.

Why: Creditworthy point (1) but no linked effect on the accuracy of the representation, so only one mark.

No marks0/2

It takes more samples every second, so the wave is stored in more detail.

Why: Confuses bit depth with sample rate, so no mark is awarded.

8Discuss6 marksImages Swap Remove

A school is creating a small logo to display on its website. The logo is stored as a bitmap image. Each pixel in the logo is stored as a binary value.

Discuss how the bitmap image of the logo is represented in binary.

Your answer should include:

pixels
binary values
the grid of pixels.

[6 marks]

Mark scheme

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.

Example answers and how they were marked

Full marks6/6

A bitmap is a grid of pixels. Each pixel is one small area of the logo and has a single colour. The width and height of the grid are measured in pixels, so the logo's dimensions tell us how many pixels it contains. Each pixel's colour is stored as a binary value. The number of bits used for each pixel is the colour depth, and with n bits there are 2^n possible values, so 2^n possible colours. For example, 3 bits per pixel would allow 8 colours. The binary values are stored row by row so that the computer can rebuild the grid. A larger grid stores more pixel values, but it can show more detail. More bits per pixel let the logo use more colours, such as the school's colours.

Why: Covers pixels as the smallest areas of a grid (AO1), binary values with colour depth and 2^n colours (AO1), and applies these to the logo's grid and colours (AO2). Sustained and structured, so Level 3.

Some marks4/6

A bitmap is a grid of pixels. Each pixel is a small square with one colour. Each pixel is stored as a binary value. The logo needs a binary value for every pixel, so a bigger logo has more values. More bits per pixel means more colours.

Why: Gives pixels and binary values, with a simple link to the logo's size. Points are mostly independent and not developed into a full discussion, so Level 2.

Some marks1/6

A bitmap image is a grid of pixels. Resolution is the number of colours in the image. Each pixel is stored as a letter, so the logo can use any colour.

Why: One basic point: a bitmap is a grid of pixels. The rest is incorrect: resolution is not the number of colours, and pixel values are stored as binary, not letters.

Edexcel GCSE Computer Science (1CP2) Exam Questions

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Questions by topic

2.1 Binary

2.2 Data representation

2.3 Data storage and compression

3.1 Hardware

3.2 Software

3.3 Programming languages

4.1 Networks

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