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GCSEComputer ScienceAQARevision Notes5. Boolean LogicBoolean LogicCombining Boolean Operators

Combining Boolean Operators (AQA GCSE Computer Science)

Revision Note

Robert Hampton

Written by: Robert Hampton

Reviewed by: James Woodhouse

Combining Boolean Operators

  • Boolean operators can be combined to produce more complex expressions

  • The combination of two or more Boolean operators forms a logic expression

  • Brackets are used to clarify the order of operations

  • A logic diagram is a visual representation of combinations of Boolean operators within a logic circuit

  • An example would be Q = NOT(A OR B) // Q space equals open parentheses top enclose A plus B end enclose close parentheses

logic circuit1

  • In the diagram above, the inputs are represented by A and B

  • P is the output of the OR gate on the left and becomes the input of the NOT gate

  • Q is the final output of the logic circuit

  • This is a logic diagram for the Boolean expression Q = NOT(A OR B) // Q space equals space open parentheses top enclose A plus B end enclose close parentheses 

Examiner Tips and Tricks

You may be asked to draw a logic circuit from a logic statement or a Boolean expression OR write the logical expression that is expressed in the logic diagram using Boolean expression operators

Logic circuits will be limited to a maximum of three inputs and one output

Example of combining Boolean operators

10-boolean-logic

  • P = (A OR B) AND NOT C // P space equals space open parentheses A plus B close parentheses space. space top enclose C

Worked Example

A green light (G) in a game switches on if all of the following conditions are true:

  • sensor D is off

  • sensor L is off

  • sensor W is on

Write a Boolean expression for this logic circuit.

You must use Boolean expression operators in your answer [3]

Answer

  • D̅. L̅. W // (D̅. W). (L̅. W) 

Guidance

  • 2 marks if fully correct but using different notation, e.g. NOT D AND NOT L AND W

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    Author
    Reviewer
    Robert Hampton

    Author: Robert Hampton

    Expertise: Computer Science Content Creator

    Rob has over 16 years' experience teaching Computer Science and ICT at KS3 & GCSE levels. Rob has demonstrated strong leadership as Head of Department since 2012 and previously supported teacher development as a Specialist Leader of Education, empowering departments to excel in Computer Science. Beyond his tech expertise, Robert embraces the virtual world as an avid gamer, conquering digital battlefields when he's not coding.

    James Woodhouse

    Author: James Woodhouse

    Expertise: Computer Science

    James graduated from the University of Sunderland with a degree in ICT and Computing education. He has over 14 years of experience both teaching and leading in Computer Science, specialising in teaching GCSE and A-level. James has held various leadership roles, including Head of Computer Science and coordinator positions for Key Stage 3 and Key Stage 4. James has a keen interest in networking security and technologies aimed at preventing security breaches.