AQA · GCSE · Computer Science
Course version: 8525 · Version from Sept 2020
Boolean logic: NOT
The supplied statement for this row is incomplete: it contains only the word NOT and no further specification text.
Checked against the AQA 8525 specification (opens in a new tab) on .
- Point 2 of 16
Study notes
From the checked teaching notes for this specification point.
The idea
The supplied statement for this row is incomplete: it contains only the word NOT and no further specification text. Treat the published scope as limited to what is shown and do not assume missing wording. In Boolean logic, NOT is a logical operator that inverts a single input: if the input is true the output is false, and if the input is false the output is true. It is a unary operator, so it takes one operand, unlike AND and OR which combine two. A truth table for NOT has two rows, one for input 0 giving output 1 and one for input 1 giving output 0. Because the full criterion is not present, revise the general behaviour of NOT and how it appears in logic diagrams and truth tables, but do not invent additional requirements that the source does not state.
What earns the marks
- NOT is a unary Boolean operator that inverts its single input.
- Input 0 produces output 1, and input 1 produces output 0.
- A NOT gate is drawn as a single input with an inverted output, and its truth table has two rows.
- NOT differs from AND and OR because it takes one operand rather than combining two.
- The supplied statement is incomplete, so only the behaviour of NOT itself should be assumed.
Common mistakes and how to put them right
Treating NOT as a two-input operator like AND or OR: NOT takes exactly one input.
Reversing the truth table so that input 0 gives output 0.
Put it right: The correct result is that the output is always the opposite of the input.
Assuming the incomplete statement implies extra content such as combined gates.
Put it right: Only the behaviour of NOT is supported by the supplied text.
Confusing the NOT gate symbol with the AND gate symbol.
Put it right: The NOT gate has a small circle at its output.
Exam tips
- Write out the two-row truth table for NOT from memory before answering.
- Check whether the question gives one input or two; NOT applies to a single input only.
- If an option describes NOT as combining two values, eliminate it.
- Do not add requirements beyond the supplied statement; answer only what is asked.
Try the lesson
The start of the Boolean logic: NOT lesson, made from checked teaching notes for this specification point.
Have a go first
A logic gate receives the single input 0. What is the output of a NOT gate for this input?
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of Boolean logic: NOT
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge