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Edexcel GCSE Computer Science (1CP2) Exam Questions

Build a practice paper from 693 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.

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4 questions · 7 marks

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1Short recall1 markSound Swap Remove

Digital sound is made up of samples.

Define the term 'bit depth'.

[1 mark]
Mark scheme

Award one mark for:

  • The number of bits used per sample (1)

Allow bits per sample

Allow the number of bits used to record/store each sample

Do not accept the number of samples taken per second (sample rate)

Do not accept the number of bits used to store the whole sound file

Do not accept the number of levels/amplitude values a sample can take

Example answers and how they were marked
Full marks1/1

The number of bits used to record each sample.

Why: States the number of bits per sample (1).

No marks0/1

The number of samples taken each second.

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

No marks0/1

The number of amplitude values each sample can take.

Why: Gives the number of levels/amplitude values, not the number of bits per sample; do not accept.

2Short recall2 marksCharacter Sets Swap Remove

ASCII is a character set that uses 7 bits to represent each character.

Give two limitations of 7-bit ASCII when it is used to represent text.

[2 marks]
Mark scheme

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

  • (Only) 128 different characters can be represented / 7 bits give 2^7 = 128 different codes (1)
  • It cannot represent characters from languages other than English / non-English alphabets, e.g. Greek, Chinese (1)
  • It cannot represent accented characters, e.g. é, ñ (1)
  • It cannot represent symbols or emoji that are not in the ASCII character set (1)

Award a maximum of one mark for the last three bullets, as they are all examples of characters that fall outside the 128 ASCII codes.

Allow 'it can only represent 128 characters, so some characters are missing' for the first bullet.

Do not accept 'it uses 7 bits' / 'it only uses 7 bits' on its own, without saying what this limits.

Do not accept 'it can only store a limited amount of text' / 'it can only store short messages', as 7 bits limits the number of characters available, not the length of a message.

Do not accept 'it can only represent the characters in the ASCII character set', as this repeats the question.

Do not accept 'it is old/out of date' or 'it cannot store numbers'.

Example answers and how they were marked
Full marks2/2

Only 128 different characters can be represented, so it cannot store characters from other languages such as Greek.

Why: 128 character limit (1) and characters from other languages (1); two separate creditworthy limitations.

Some marks1/2

It cannot show accented characters like é and it only uses 7 bits.

Why: Accented characters (1); 'only uses 7 bits' is not qualified, so scores 0.

No marks0/2

It only uses 7 bits, so it can only store a small amount of text.

Why: Scores 0: text length is not a limitation of 7-bit ASCII, and 'only uses 7 bits' is unqualified; both Do not accept lines apply.

3Describe2 marksSound Swap Remove

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

Describe how bit depth affects the stored value of a sound sample.

[2 marks]
Mark scheme

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.

Example answers and how they were marked
Full marks2/2

The bit depth is the number of bits used to store each sample, so a higher bit depth gives more possible values for the amplitude that can be stored.

Why: First point, the number of bits per sample (1), then the linked development, more possible values for the amplitude (1).

Some marks1/2

The bit depth is the number of bits used to store one sample.

Why: Gives the first point, the number of bits per sample (1), but does not develop how this affects the value that is stored.

No marks0/2

A higher bit depth makes the sound better quality and more accurate.

Why: Near-miss: 'better quality' and 'more accurate' on their own, with no development linked to the number of values or the amplitude, so no mark is awarded.

4Explain2 marksCharacter Sets Swap Remove

The ASCII code for the uppercase letter A is 65, which is stored as the 7-bit pattern 1000001.

Explain why the lowercase letter a is stored using a different 7-bit pattern.

[2 marks]
Mark scheme

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

  • The computer needs to tell/distinguish the uppercase A from the lowercase a (1) because each different character has its own unique 7-bit code/pattern (1)
  • A and a are different characters (1) so each needs a different 7-bit pattern to be stored and displayed correctly (1)
  • If A and a had the same 7-bit pattern (1) the computer could not tell which character to display (1)

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

Do not accept 'because they are different letters/cases' without saying they need different/unique codes or that the computer must tell them apart.

Do not accept 'because A is a capital letter' on its own.

Do not accept 'because the codes are different numbers' or '65 is not 97' without linking to the need to tell the characters apart or to unique codes.

Example answers and how they were marked
Full marks2/2

Each character needs its own unique code, so the computer can tell that A and a are different characters and display the right one.

Why: Gives the point that the computer must tell A and a apart (1) and links it to the reason that each character needs its own unique code (1).

Some marks1/2

The computer must be able to tell the difference between uppercase and lowercase letters.

Why: Gives the point that the computer must tell the two characters apart (1) but gives no linked reason about unique codes or different 7-bit patterns.

No marks0/2

Because A is a capital letter and a is lowercase.

Why: Only states that the letters are different cases, which the mark scheme says is not accepted without saying they need unique codes or that the computer must tell them apart.

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