GCSE · Computer Science · AQA · Spec 8525

AND logic gate

One gate, two inputs, one rule — AND is the gatekeeper of Boolean logic.

What you need to know

  • AND outputs 1 only when ALL inputs are 1 — any 0 input gives a 0 output.
  • The truth table for a two-input AND gate has four rows (00, 01, 10, 11) with only the last row outputting 1.
  • The Boolean expression for AND is written as A·B or A AND B.
  • AND gates can have more than two inputs — ALL must be 1 for the output to be 1.

The big picture

The AND logic gate outputs TRUE (1) only when ALL of its inputs are TRUE (1). If any input is FALSE (0), the output is always FALSE (0). This mirrors everyday language: 'You can enter IF you have a ticket AND an ID.' AND gates are fundamental building blocks of digital circuits, used in everything from CPUs to security systems.

TONIGHT'S REVISION

AND Logic Gate

Output is 1 only when ALL inputs are 1 — the gatekeeper of Boolean logic.

Computer Science · Logic gates

Logic gates — build the truth table

Toggle inputs A and B — watch when the AND gate outputs 1 and compare with OR and XOR.

ABAND0
ABAND out
000
010
100
111

Predict, then check

Read the inputs carefully before committing — AND is strict.

A two-input AND gate has A = 1 and B = 0. Before checking the truth table, what is the output?

How the AND gate processes its inputs

Follow one signal through — notice where a single 0 stops everything.

AND vs OR — know the difference

AND gatevsOR gate

This is the most common mix-up in logic gate questions.

Focus

Output rule

AND gate

ALL inputs must be 1

OR gate

AT LEAST ONE input must be 1

The insight

AND is stricter — a single 0 kills the output; OR is more permissive — a single 1 is enough.

Rows outputting 1 (2-input table)

AND gate

1 row only (row 1,1)

OR gate

3 rows (01, 10, 11)

Boolean symbol

AND gate

A · B (dot)

OR gate

A + B (plus)

Real-world analogy

AND gate

Need ticket AND ID to enter

OR gate

Need ticket OR student card to enter

Cross-subject · Exam skill

Command Word Coach

AND logic gate — AQA exam language

CompleteBloom · Apply

01Definition

Fill in every missing cell of a truth table following the gate's rule exactly.

02Mark-band signal

A strong answer covers every input combination and gets every output cell correct.

03Sentence stems

  • Complete the truth table for the AND gate below.
  • Complete the truth table to show the output for each combination of inputs.

04Common mistake

Leaving a row out or repeating one — working in binary counting order (00, 01, 10, 11) helps you cover all four.

Exam line: Completing a truth table is a common AND-gate task. Work through the input combinations systematically and remember that only 1 AND 1 gives an output of 1. You may also be asked to write the Boolean expression: AND is written as a dot, so A AND B is A.B
Watch out: The command word is a guide to how much to write: 'State' asks for a fact, while 'Explain' asks for a rule and a reason. Match your answer to the command.

Key points

1AND = ALL inputs must be 1 to get output 1.
2Truth table: 0 AND 0 = 0, 0 AND 1 = 0, 1 AND 0 = 0, 1 AND 1 = 1.
3Symbol: a D-shaped flat-back gate with two input lines on the left.
4Boolean notation: A · B (dot means AND) or simply A AND B.
5Real-world use: a door alarm that only triggers if the door is open AND motion is detected.

Worked example

Problem

A security system uses an AND gate. Input A = door sensor (1 = open), Input B = motion sensor (1 = motion detected). What is the output when the door is closed (A=0) and motion is detected (B=1)?

🧠

Memory hook

Think of AND as a bouncer with TWO rules — you need BOTH to get in. No ticket? Out. No ID? Out. Both? Welcome.

★ Exam tip

When you complete a truth table for an AND gate, working through the input combinations systematically (00, 01, 10, 11) helps make sure you do not miss a row. Remember that only 1 AND 1 gives an output of 1.

⚠ Watch out

Confusing AND with OR — AND needs ALL inputs to be 1; OR only needs ONE input to be 1.

✓

Check yourself

Without looking — what is the only input combination for a two-input AND gate that gives an output of 1?

Flashcards

(22)
What does an AND gate output when both inputs are 1?
1 (TRUE)
What does an AND gate output when one input is 0 and one is 1?
0 (FALSE)
What does an AND gate output when both inputs are 0?
0 (FALSE)
How many rows are in the truth table for a two-input AND gate?
4 rows: 00, 01, 10, 11
Write the Boolean expression for an AND gate with inputs A and B.
A · B (read as A AND B)
Which row in the AND truth table gives an output of 1?
Only the row where A=1 AND B=1 gives output 1
What is the shape of the AND gate symbol?
A D-shape with a flat back — inputs on the left, curved output side on the right
How does AND differ from OR?
AND needs ALL inputs to be 1; OR only needs at least ONE input to be 1
What is the output of the AND gate when A=1 and B=0?
0 — because B is 0 and AND requires all inputs to be 1
What is the output of the AND gate when A=1 and B=1?
1 — this is the only combination where AND outputs 1
Give a real-world analogy for an AND gate.
A door that only opens when you have BOTH a keycard AND a correct PIN
Can an AND gate have more than two inputs?
Yes — all inputs must still be 1 for the output to be 1
What is the output of a three-input AND gate when inputs are 1, 1, 0?
0 — all three inputs must be 1; a single 0 forces the output to 0
In Boolean algebra, what symbol represents AND?
A dot · for example A · B
How many outputs of 1 appear in the full two-input AND truth table?
Exactly one — only when A=1 and B=1
Write the full truth table for a two-input AND gate.
A=0,B=0 → Output=0 | A=0,B=1 → Output=0 | A=1,B=0 → Output=0 | A=1,B=1 → Output=1
What does HIGH and LOW mean in logic gate contexts?
HIGH = 1 (TRUE), LOW = 0 (FALSE)
A three-input AND gate has inputs A=1, B=1, C=1. What is the output?
1 — all inputs are 1, so the AND condition is satisfied
Why is the AND gate useful in CPU instruction decoding?
It allows the CPU to act only when multiple specific conditions are all true simultaneously
What is the output of NOT(A AND B) when A=1 and B=1?
0 — AND gives 1, then NOT inverts it to 0.
Which gate has exactly ONE output of 1 in its two-input truth table?
AND gate — only the row 1,1 gives output 1
State the AND gate rule in one sentence.
Output is 1 only when ALL inputs are 1; any 0 input makes the output 0

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

Learn AND logic gate properly — interactive practice, marked questions and flashcards.

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