Apply the NOT gate
Invert a single Boolean input and complete a NOT truth table.
Exam scope and assessment notes
This original learning sequence follows Topic 10 of Cambridge IGCSE Computer Science 0478, 2026–2028 syllabus Version 6. It covers standard symbols and functions for NOT, AND, OR, NAND, NOR and XOR/EOR, and translation among statements, expressions, circuits and truth tables. NOT has one input; other gates have at most two. Circuit practice is limited to three inputs and one output and keeps the requested design without simplification. Lessons and checks support learning but do not award an official Cambridge grade. Full timed-paper practice, practical programming in an executable workspace and human subject-teacher review remain outstanding; the separate 2029–2031 syllabus is not mapped here.
Before you begin
- Be able to read binary 0 and 1 as the two possible logic values. Each lesson introduces the gate or translation skill it uses.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
How many inputs does NOT take?
What you will learn
- Apply NOT to 0 and 1
- Complete a one-input truth table
- Write the NOT expression
Core idea
NOT is the only single-input gate in this syllabus. It reverses the input: NOT 0 is 1, and NOT 1 is 0. If the input is A, the output expression can be written NOT A or ¬A.
In a logic circuit, 1 represents TRUE and 0 represents FALSE. A gate applies a defined rule to its input value or values and produces one binary output.
A reliable method
List the two possible input values, 0 then 1, and write the opposite value in the output column. With a circuit, trace the input into the NOT gate and invert it once; do not change a different input by mistake.
Keep the given statement, expression, diagram or table in view while working. Check each row or connection against the rule, and preserve the stated circuit structure; the syllabus does not ask you to simplify it.
Pause and explain
If A=1, what value leaves a NOT gate?
Worked example
Complete the output for Y = NOT A when A is 0, then 1.
Show the worked solution
- Write the possible A values: 0 and 1.
- NOT reverses each value.
- The output column is 1, then 0.
Answer A: 0, 1; Y: 1, 0.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Write the truth table for Y=NOT A.
Give me a hint
There are two possible values for A.
Compare my reasoning
- First row: A=0, so Y=1.
- Second row: A=1, so Y=0.
- Keep the rows in the listed order.
A | Y: 0 | 1; 1 | 0.
Look for these in your work
- Both input rows
- Outputs inverted
An alarm output is active when the door is closed input C is 0. Write an expression for the output.
Give me a hint
The output should be the opposite of C.
Compare my reasoning
- The required output is 1 when C=0.
- A NOT gate produces 1 exactly when C=0.
- Use one input and invert it.
Alarm = NOT C.
Look for these in your work
- Input named
- NOT applied
A sensor sends A=1 when a window is shut. A warning lamp must turn on only when it is open. State the gate and output for A=0 and A=1.
Give me a hint
The lamp condition is the opposite of the sensor's stated meaning.
Compare my reasoning
- The lamp should output 1 for A=0.
- Use NOT A.
- For A=1, the lamp output is 0.
Use NOT; outputs are 1 for A=0 and 0 for A=1.
Look for these in your work
- Context translated
- Both cases correct
Common mistakes
- Copying A instead of reversing it
- Adding a second input to a NOT gate
- Inverting twice when only one NOT gate is shown
What can you explain now?
If A=0, what is NOT A?
Compare with the explanation
1
NOT changes the input 0 into the opposite value, 1.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
What are the two rows of a NOT truth table?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.