← IGCSE Computer Science Paper 2

The OR gate

The OR gate has two inputs, A and B. Its output X is 1 when at least one input is 1, and 0 only when both are 0. Its truth table output column is 0 1 1 1.

Part of: IGCSE Computer Science 0478 — 10 Boolean Logic — Module 8

Understanding The OR gate in IGCSE Computer Science Paper 2

What it does: The output is 0 for the row 0,0 and 1 for the other three rows, because at least one input is 1 in each of them. The expression names both inputs A and B and the output X, joined by the word OR. OR outputs 1 if A is 1, B is 1, or both. Only AND needs both inputs to be 1. The OR gate is written X = A OR B. X = A AND B is the expression for an AND gate. One input is 1, which is at least one, so the OR gate outputs 1.

Common mistakes: The OR gate output column is 0 1 1 1 because X is 1 whenever at least one input is 1. The column 0 0 0 1 belongs to the AND gate. Logic gate inputs are single bits, so B can only be 0 or 1. The line should be B <- 0.

Class: _____________________ · Name: _____________________ · Date: _________

Free printable worksheet with full answer key — or add this module to a class and your students practise it interactively.

🖨 Print worksheet + answer key Add The OR gate to a class →

This module's key terms are also in a printable crossword (Modules 539–551) and word search (Modules 539–580).

Take this worksheet further — free with Cloodit

Each concept is reinforced from every angle — learned, then applied, then tested.

Learning

Duo

Which statement describes the OR gate output?

X is 1 when at least one input is 1X is 1 only when both inputs are 1

Matches

A=1, B=0 -> X = 0 (OR gate)

↓

An OR gate outputs 1 when at least one input is 1, so A=1 and B=0 gives X = 1, not 0.

Applying

Meanings

Term

X = A OR B

Meaning

The OR gate has two inputs, A and B. Its output X is 1 when at least one input is 1, and 0 only when both are 0. Its truth table output column is 0 1 1 1.

Practice

X = A OR B

Testing

Gaps

X = A B

Check Answer

Spots

2Inputs: A and B

3Output column: 0 0 0 1

Cloodit turns curriculum-aligned coding content into journeys students work through one biome at a time.

Students earn collectable badges

Over 100 of them, across seven natural biomes.

Study Buddy

Students build a real study resource

Turns their work into revision material ready for Flash Cards and Exam study.

Diamond Dash — one of Cloodit's live, competitive Sprint games

Students lock in with Sprints

Live, competitive practice for the start of the lesson or a teacher-led lesson finisher.

A Cloodit certificate of achievement, ready to personalise and print

Custom printable certificates

Honour your top performers, or encourage a student who's trying hard — ready to print in seconds.

Add to class →

Quick Questions

1. Which statement describes the OR gate output?

A. X is 1 when at least one input is 1 ✓

B. X is 1 only when both inputs are 1

OR outputs 1 if A is 1, B is 1, or both. Only AND needs both inputs to be 1.

2. Which is the correct logic expression for an OR gate with inputs A and B and output X?

A. X = A AND B

B. X = A OR B ✓

The OR gate is written X = A OR B. X = A AND B is the expression for an AND gate.

3. Which output column (X) is correct for an OR gate for rows A,B = 00, 01, 10, 11?

A. 0 1 1 1 ✓

B. 0 0 0 1

OR gives 0 only when both inputs are 0, so the column is 0 1 1 1. The column 0 0 0 1 belongs to AND.

4. A = 0 and B = 1 go into an OR gate. What is X?

A. X = 1 ✓

B. X = 0

One input is 1, which is at least one, so the OR gate outputs 1.

5. A = 0 and B = 0 go into an OR gate. What is X?

A. X = 1

B. X = 0 ✓

The OR gate outputs 0 only when neither input is 1, so both inputs being 0 gives X = 0.

Match the Pairs

X = A OR B → The output X is 1 when A is 1, when B is 1, or when both are 1.

A=0, B=0 -> X = 0 → The only input row where an OR gate outputs 0, because neither input is 1.

The truth table output column for an OR gate with inputs 00, 01, 10, 11 in order → 0 1 1 1

The OR gate has two inputs called A and B and one output called X → X = A OR B

A=1, B=0 -> X = 0 (OR gate) → An OR gate outputs 1 when at least one input is 1, so A=1 and B=0 gives X = 1, not 0.

OR truth table output: 0 0 0 1 → 0 0 0 1 is the output column for AND. The OR gate output column is 0 1 1 1.

Key Term

X = A OR B

The OR gate has two inputs, A and B. Its output X is 1 when at least one input is 1, and 0 only when both are 0. Its truth table output column is 0 1 1 1.

Fill in the Blanks

1. X = A OR B

Hint: Type the gate name that joins A and B so the output is 1 when at least one input is 1.

2. X = A OR B

Hint: Type the label used for the output of the gate.

3. A = 1, B = 0 -> X = 1

Hint: Type the output bit when only one input is on.

4. A = 0, B = 0 -> X = 0

Hint: Type the output bit when neither input is on.

5. OR truth table X column: 0 1 1 1

Hint: Type the output bit for the last row, where both inputs are on.

Spot the Error

Question 1

A Gate: OR

B Inputs: A and B

C Output column: 0 0 0 1

Line C — The OR gate output column is 0 1 1 1 because X is 1 whenever at least one input is 1. The column 0 0 0 1 belongs to the AND gate.

Question 2

A A <- 1

B B <- 2

C X <- A OR B

D OUTPUT X

Line B — Logic gate inputs are single bits, so B can only be 0 or 1. The line should be B <- 0.

Question 3

A Gate: OR

B Inputs: A and B

C Output X is 1 if A and B are 1

Line C — An OR gate gives 1 when at least one input is 1, not only when both are 1. The line should say 'Output X is 1 if A or B is 1'.

Question 4

A A B | A OR B

B 0 0 | 0

C 0 1 | 1

D 1 0 | 0

E 1 1 | 1

Line D — In the OR truth table, A = 1 and B = 0 gives X = 1 because at least one input is 1. The row should be 1 0 | 1.

Question 5

A Expression for OR gate:

B X = A AND B

C Inputs: A and B

Line B — The expression for the OR gate is X = A OR B. X = A AND B is the expression for the AND gate.

Student with a class code? Join your class →