AQA
A-level
COMPUTER SCIENCE
7517/2
Paper 2
Version: 1.0 Final
*JUN237517201*
IB/G/Jun23/E7 7517/2
For Examiner’s Use
Question
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Monday 19 June 2023 Morning Time allowed: 2 hours 30 minutes
Materials
For this paper you must have:
• a calculator.
Instructions
• Use black ink or black ball-point pen.
• Fill in the boxes at the top of this page.
• Answer all questions.
• You must answer the questions in the spaces provided. Do not write outside
the box around each page or on blank pages.
• If you need extra space for your answer(s), use the lined pages at the end of
this book. Write the question number against your answer(s).
• Do all rough work in this book. Cross through any work you do not want to
be marked.
Information
• The marks for questions are shown in brackets.
• The maximum mark for this paper is 100.
Advice
• In some questions you are required to indicate your answer by completely
shading a lozenge alongside the appropriate answer as shown.
• If you want to change your answer you must cross out your original answer as
shown.
• If you wish to return to an answer previously crossed out, ring the answer
you now wish to select as shown.
Please write clearly in block capitals.
Centre number Candidate number
Surname
Forename(s)
Candidate signature
I declare this is my own work.
A-level
COMPUTER SCIENCE
Paper 2
2
*02*
IB/G/Jun23/7517/2
Do not write
outside the
Answer all questions. box
0 1 . 1 A sound is sampled and recorded digitally. The sound is sampled at a rate of 48 000
samples per second (Hz) for 3 minutes using a 16-bit sample resolution.
Calculate the size of the digital recording, giving your answer in mebibytes.
Give your answer rounded to 2 decimal places.
You should show your working.
[2 marks]
Answer mebibytes
0 1 . 2 The highest frequency component in a different sound is 15 000 Hz.
What is the minimum sampling rate that should be used when recording this sound to
ensure that all the frequencies in the original waveform are preserved, so that when
the recording is played back the original sound is recreated accurately?
[1 mark]
Answer Hz
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0 1 box . 3 Figure 1 shows part of the process of playing back a sound that has been sampled.
The binary sound data is used to generate an electrical waveform.
Figure 1
A hardware component on a sound card carries out the process shown in Figure 1.
State the name of this component.
[1 mark]
Turn over for the next question
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IB/G/Jun23/7517/2
Do not write
outside the
box 0 2 Figure 2 shows some of the fields contained in a packet, transmitted on a
computer network.
Figure 2
Destination
Address
Source
Address Payload (data) Checksum
0 2 . 1 Name two fields typically included in a packet which are not shown in Figure 2.
[2 marks]
Field 1
Field 2
0 2 . 2 Explain what the checksum is used for and outline how the checksum’s value will
be determined.
[2 marks]
Explain what the checksum is used for
Outline how the checksum’s value will be determined
0 2 . 3 Packets of data are transmitted using packet switching.
Describe the role of a router in packet switching.
[2 marks]
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0 3 box . 1 Encrypt the plaintext SECURITY using the Caesar cipher with a key of 4.
[1 mark]
Plaintext Ciphertext
SECURITY
The Caesar cipher is an example of a substitution cipher.
A different substitution cipher encrypts letters using the method shown in Figure 3.
Figure 3
Plaintext A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Ciphertext C D J R K Y G S Q F E P W O H V L I U Z T B N A X M
0 3 . 2 State one weakness that both the Caesar cipher and the cipher shown in Figure 3
have which means they can be easily cracked.
[1 mark]
0 3 . 3 State one reason why the cipher in Figure 3 is harder to crack than the
Caesar cipher.
[1 mark]
Question 3 continues on the next page
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box 0 3 . 4 The Vernam cipher, unlike the Caesar cipher, can be perfectly secure.
State two conditions that must be met for the Vernam cipher to offer perfect security.
[2 marks]
Condition 1:
Condition 2:
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*07*
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