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Edexcel GCSE Computer Science (1CP2) Exam Questions

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3 questions · 10 marks

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1Explain2 marksSound Swap Remove

The same sound is recorded twice using different sample intervals.

Explain the effect of using a longer sample interval on the digital recording.

[2 marks]
Mark scheme

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

  • Fewer samples are taken every second (1) so less detail of the sound wave is captured (1)
  • Fewer samples are taken every second (1) so the file is smaller/uses less storage space (1)
  • The wave is measured less often (1) so parts/changes in the wave between samples are missed (1)

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

The 'fewer samples are taken/measured less often' point can only be credited once; the second mark is for a valid expansion linked to it.

Do not accept restating the question, e.g. 'the time between measurements is longer' or 'the sample interval is longer', as either the point or the expansion.

Do not accept 'the sample rate is lower' as the expansion, as this says the same thing as a longer sample interval.

Do not accept 'the sound is lower quality/less accurate' on its own without saying what is lost, e.g. less detail of the wave captured/parts of the wave missed.

Do not accept answers about using fewer bits per sample or about compression, as these do not follow from the sample interval.

Example answers and how they were marked
Full marks2/2

Fewer samples are taken every second, so less detail of the sound wave is captured and the recording is less accurate.

Why: Point (fewer samples each second) (1) with linked reason (less detail of the wave captured) (1).

Some marks1/2

Fewer samples are taken every second.

Why: Creditworthy point (1) but no linked effect on the detail or size of the recording, so only one mark.

No marks0/2

The samples are stored using fewer bits, so the sound is less accurate.

Why: Describes a smaller bit depth rather than a longer sample interval, so no mark is awarded.

2Explain2 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 because two bits give four possible binary values.

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.

3Discuss6 marksSound Swap Remove

A developer is creating a voice memo app for a phone. The app records speech and saves it as a digital audio file. The developer can choose the bit depth used for each sample.

Discuss how the bit depth affects how the amplitude of the speech is represented in binary and the size of the saved file.

Your answer should include:

  • how the amplitude of a sample is stored using bits
  • how the bit depth affects the accuracy of each sample
  • the effect of the bit depth on the file size.
[6 marks]
Mark scheme

Indicative content

Storing amplitude

  • Each sample records the amplitude of the sound wave at that moment, and the amplitude is stored as a binary number.
  • The bit depth is the number of bits used to store each sample, so it sets how many different amplitude values can be represented.
  • With a bit depth of 8, there are 2^8 = 256 possible values for the height of the wave.
  • The binary value for each sample tells the computer how loud the speech is at that point.

Accuracy

  • A higher bit depth gives more possible values, so the recorded amplitude can be closer to the true amplitude of the speech.
  • With a low bit depth, the amplitude must be rounded to the nearest available value, which adds quantisation error and makes the speech sound rough.
  • A higher bit depth reduces the difference between the original wave and the digital version.
  • Quiet parts of the speech may be lost or inaccurately recorded if the bit depth is too low.

File size

  • A higher bit depth uses more bits for every sample, so the voice memo file is larger.
  • A lower bit depth reduces the number of bits per sample, so the file is smaller and uses less storage on the phone.
  • The developer must balance clear speech against storage space and download time.

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 link the bit depth to both the accuracy of the amplitude and the file size.

Do not accept bit depth defined as the number of samples taken per second.

Example answers and how they were marked
Full marks6/6

Each sample measures the amplitude of the speech wave and stores it as a binary number. The bit depth is the number of bits used for each sample, so with 4 bits there are only 16 possible amplitude values, but with 16 bits there are 65,536. A higher bit depth therefore lets the app record the loudness of the speech more accurately, because each sample can be closer to the real wave and quiet sounds are less likely to be rounded away. This makes the voice memo sound clearer. However, every sample uses more bits, so a higher bit depth creates a larger file, which takes up more storage on the phone and may take longer to send. The developer should choose a bit depth that keeps speech clear without making the files unnecessarily large.

Why: Level 3 (6 marks): explains amplitude stored in binary, how bit depth gives more values and accuracy, and the file-size trade-off, applied to the voice memo app.

Some marks3/6

The bit depth is the number of bits used for each sample. A higher bit depth means the amplitude can be stored more accurately because there are more values. But it makes the file larger. The app should use a high bit depth for clear speech.

Why: Level 2 (3 marks): covers bit depth, accuracy and file size briefly with some linkage, but lacks detailed reasoning.

Some marks1/6

The bit depth is the number of samples taken per second. A higher bit depth means more samples are taken, so the file is smaller and the speech is more accurate.

Why: Level 1 (1 mark): a basic idea that more accuracy is linked to higher bit depth, but bit depth is confused with sample rate and the file-size effect is wrong.

Questions by topic

2.1 Binary

Build a paper on this topic 58
Adding Binary Numbers 6 questions Binary and Hexadecimal Basics 10 questions Binary Shifts 6 questions Binary to Denary Conversion 6 questions Binary to Hexadecimal Conversion 6 questions Denary to Binary Conversion 6 questions Denary to Hexadecimal Conversion 6 questions Denary to Negative Binary Conversion 6 questions Hexadecimal to Binary Conversion 6 questions

2.2 Data representation

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Character Sets 18 questions Images 19 questions Sound 19 questions

2.3 Data storage and compression

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Compression 18 questions Units & Conversion 6 questions

3.1 Hardware

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Embedded Systems 17 questions Fetch Decode Execute Cycle 15 questions Primary Memory 15 questions Secondary Memory 15 questions Stored Program Computers 15 questions

3.2 Software

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File Management 18 questions Memory Management 16 questions Peripheral Management 11 questions Process Management 12 questions Purpose & Function of Operating Systems 17 questions Software Basics 13 questions User Management 18 questions Utility Software 19 questions

3.3 Programming languages

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Low and High Level Languages 19 questions Translators 18 questions

4.1 Networks

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Addressing 16 questions LANs & WANs 16 questions Network Speed 5 questions Packet Switching 16 questions Protocols & Layers 17 questions The Internet 16 questions Topologies 17 questions Wired Connections 17 questions Wireless Connections 18 questions

4.2 Network security

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Network Security Risks 18 questions Preventing Network Security Risks 18 questions

5.1 Environmental

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E-waste 17 questions Manufacturing Technology 19 questions

5.2 Ethical and legal

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Data Protection Act 17 questions Impact of AI 18 questions Intellectual Property 18 questions Software Licences 18 questions

5.3 Cybersecurity

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Malware 18 questions Social Engineering 18 questions

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