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Logic gates: AND, OR and NOT sheet
3-mark answer frame

Draw the logic symbols and write the truth tables of AND, OR and NOT gates. Explain how AND and OR gates can be shown with switches.

How to lay out the answer. Follow the frame, then write it in your own words.

  1. 1 · Define a logic gate. A logic gate is a circuit with one or more inputs and one output that follows Boolean logic on the bits 0 and 1.
  2. 2 · AND gate. Y = A·B; the output is 1 only when A and B are both 1; shown by switches in series.
  3. 3 · OR gate. Y = A + B; the output is 1 when A or B or both are 1; shown by switches in parallel.
  4. 4 · NOT gate. Y = Ā; the output is opposite to the input; made with a transistor switch.
  5. 5 · Draw the symbols and tables. [Symbols: D-shaped AND, shield-shaped OR, triangle with a bubble for NOT; truth tables with every input combination]
  6. 6 · Real life. A washing machine that starts only when the door is shut and the button is pressed uses AND logic.
  7. 7 · Close in one line. So, AND needs all inputs high, OR needs any one, and NOT inverts.

Scoring tip: Write all four rows (00, 01, 10, 11) for a two-input gate. Missing a row loses the mark for that table.