COMPUTER SCIENCE
Paper 2
Please write clearly in block capitals.
Centre Candidate
number number
Surname
Forename(s)
Candidate ure
signat
A-level
COMPUTER SCIENCE
Paper 2
Tuesday 9 June 2020 Morning Time allowed: 2 hours 30 minutes
Materials
For this paper you must have:
a calculator. For Examiner’s Use
Instructions Questio Mark
n
Use black ink or black ball-point pen.
1
Fill in the boxes at the top of this page.
Answer all questions. 2
You must answer the questions in the spaces provided. Do not 3
write outside the box around each page or on blank pages.
4
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). 5
Do all rough work in this book. Cross through any work you do 6
not want to be marked. 7
8
Information
The marks for questions are shown in brackets. 9
The maximum mark for this paper is 100. 10
11
Advice
In some questions you are required to indicate your answer by TOTAL
completely shading a lozenge alongside the appropriate answer
*Jun207517201
* IB/G/Jun20/
E16
7517/2
,COMPUTER SCIENCE
Paper 2
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.
*Jun207517201
* IB/G/Jun20/
E16
7517/2
, 2
Do not write
outside the
Answer all box
questions.
0 1 .1 A sound has been sampled and recorded. The sound was sampled for 1
minute and 40 seconds at a sample rate of 8000 Hz with a 16-bit sample
resolution.
A sample rate of 1 Hz means that one sample has been taken every second.
Calculate the minimum amount of storage space, in bytes, needed to
store the sampled sound.
You should show your working.
[2 marks]
Answer
0 1 .2 An analogue to digital converter (ADC) was used during the sampling process.
Explain the principles of operation of an ADC.
[2 marks]
4
*02
IB/G/
* Jun20/7517/2
, 3
Do not write
outside the
0 2 Questions 02.2, 02.3, 02.4 and 02.5 use a normalised floating point Turn
representation with a 7-bit mantissa and a 5-bit exponent, both stored over
using two’s complement. ►
0 2
.1 Non-integer values such as -1.65 and 23/1068 can be represented by a
computer using a fixed point or a floating point system.
State one advantage of using a floating point system over a fixed point
system and
one advantage of using a fixed point system over a floating point system.
You should assume that the two systems use the same number of bits
to store a value.
[2 marks]
Advantage of floating point
Advantage of fixed point
0 2
.2 The following is a floating point representation of a number:
Calculate the decimal equivalent of the number.
Express your answer to at least four decimal places or as a fraction. You
should show your working.
[2 marks]
Answer
*03
IB/G/
* Jun20/7517/2
Paper 2
Please write clearly in block capitals.
Centre Candidate
number number
Surname
Forename(s)
Candidate ure
signat
A-level
COMPUTER SCIENCE
Paper 2
Tuesday 9 June 2020 Morning Time allowed: 2 hours 30 minutes
Materials
For this paper you must have:
a calculator. For Examiner’s Use
Instructions Questio Mark
n
Use black ink or black ball-point pen.
1
Fill in the boxes at the top of this page.
Answer all questions. 2
You must answer the questions in the spaces provided. Do not 3
write outside the box around each page or on blank pages.
4
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). 5
Do all rough work in this book. Cross through any work you do 6
not want to be marked. 7
8
Information
The marks for questions are shown in brackets. 9
The maximum mark for this paper is 100. 10
11
Advice
In some questions you are required to indicate your answer by TOTAL
completely shading a lozenge alongside the appropriate answer
*Jun207517201
* IB/G/Jun20/
E16
7517/2
,COMPUTER SCIENCE
Paper 2
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.
*Jun207517201
* IB/G/Jun20/
E16
7517/2
, 2
Do not write
outside the
Answer all box
questions.
0 1 .1 A sound has been sampled and recorded. The sound was sampled for 1
minute and 40 seconds at a sample rate of 8000 Hz with a 16-bit sample
resolution.
A sample rate of 1 Hz means that one sample has been taken every second.
Calculate the minimum amount of storage space, in bytes, needed to
store the sampled sound.
You should show your working.
[2 marks]
Answer
0 1 .2 An analogue to digital converter (ADC) was used during the sampling process.
Explain the principles of operation of an ADC.
[2 marks]
4
*02
IB/G/
* Jun20/7517/2
, 3
Do not write
outside the
0 2 Questions 02.2, 02.3, 02.4 and 02.5 use a normalised floating point Turn
representation with a 7-bit mantissa and a 5-bit exponent, both stored over
using two’s complement. ►
0 2
.1 Non-integer values such as -1.65 and 23/1068 can be represented by a
computer using a fixed point or a floating point system.
State one advantage of using a floating point system over a fixed point
system and
one advantage of using a fixed point system over a floating point system.
You should assume that the two systems use the same number of bits
to store a value.
[2 marks]
Advantage of floating point
Advantage of fixed point
0 2
.2 The following is a floating point representation of a number:
Calculate the decimal equivalent of the number.
Express your answer to at least four decimal places or as a fraction. You
should show your working.
[2 marks]
Answer
*03
IB/G/
* Jun20/7517/2
