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Ready-to-use computing activity

Logic Reverse Engineer

GCSE45-60 minutesLogic Gate Playground

Teacher overview

Prior knowledge: Learners should recognise AND, OR, XOR and NOT truth-table patterns.

Learning objective: Infer missing gates and truth-table values from observed circuit behaviour.

Starter

A circuit outputs 1 only when A and B are different. Which gate might it use?

Main task

  1. Match each output pattern to AND, OR, XOR or NOT.
  2. Complete missing truth-table values for a two-gate circuit.
  3. Build a circuit that matches the behaviour: output is 1 when A is true and B is false.
  4. Explain the circuit in one clear sentence.
  5. Swap one gate and predict how the truth table changes.

Support prompts

  • Look for the row where both inputs are 1.
  • XOR is true when inputs are different.
  • A AND NOT B means A must be true and B must be false.

Challenge

Create a circuit with three inputs where C can override the final output.

Plenary or exit question

Which clue helped you identify the missing gate fastest?

Related tool

Open Logic Gate Playground