IGCSE Computer Science Paper 2 Definitions Worksheet: 10 Boolean Logic (Modules 562–580)
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Key terms
Write what each term means, in your own words.
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X = (A AND B) OR C
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logic circuit
3
trace a circuit
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trace each row
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X = A AND B
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one gate per operator
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junction dot
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key word = gate
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X = (A AND NOT B) OR (NOT A AND B)
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3 inputs, 1 output
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equivalent
12
common logic mistakes
Answer Key
IGCSE Computer Science Paper 2 · Modules 562–580 · Student wording will vary for definitions
1X = (A AND B) OR C — Fill all 8 rows of A, B and C: work out the bracket (A AND B) in an extra column first, then combine it with C using OR to get output X.
2logic circuit — A diagram of logic gates joined by wires. Inputs are on the left, the output is on the right, and each wire carries 0 or 1. A dot where a wire splits is a junction.
3trace a circuit — Write the input values on the wires, then work gate by gate from left to right, writing each gate's output on its output wire until you reach the final output X.
4trace each row — Follow one row of input values through each gate in the circuit, write each gate's output in an extra column, then copy the final value of X into the truth table.
5X = A AND B — Name the gate, then write X = with the input letters and the gate name, e.g. an AND gate with inputs A and B is X = A AND B. NOT has one input: X = NOT A.
6one gate per operator — Draw every gate in the given expression, one for each operator, even if a shorter circuit has the same truth table. Never combine or remove gates.
7junction dot — A dot drawn where wires join, so one input can feed two gates. Wires that cross with no dot are not connected. Draw inputs on the left and the output on the right.
8key word = gate — Words in a problem statement point to a gate: both/and = AND, either/or = OR, not = NOT, neither...nor = NOR, not both = NAND, only one of = XOR.
9X = (A AND NOT B) OR (NOT A AND B) — To write an expression from a truth table, take each row with output 1 and join its inputs with AND, adding NOT to any input that is 0. Then join those rows with OR.
103 inputs, 1 output — A circuit here has at most three inputs (A, B, C) and exactly one output X. With 3 inputs the truth table has 8 rows (2 x 2 x 2). Gates with two inputs can be combined to handle the third input.
11equivalent — A circuit, expression and truth table are equivalent when each gives the same output X for the same inputs. Check by working out X row by row in each one and comparing the results.
12common logic mistakes — Mixing up NAND/AND or OR/XOR, rows out of binary order, NOT on the wrong part, missing brackets or columns, wrong input counts, or simplifying a circuit that must be drawn as given.