The OR gate

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The OR gate

Name:
Date:
Class:
A

Quick Questions

Shade in the A or B circle for each question.

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

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left columnRight column
1X = A OR B AAn OR gate outputs 1 when at least one input is 1, so A=1 and B=0 gives X = 1, not 0.
2A=0, B=0 -> X = 0 BThe output X is 1 when A is 1, when B is 1, or when both are 1.
3The truth table output column for an OR gate with inputs 00, 01, 10, 11 in order CX = A OR B
4The OR gate has two inputs called A and B and one output called X DThe only input row where an OR gate outputs 0, because neither input is 1.
5A=1, B=0 -> X = 0 (OR gate) E0 0 0 1 is the output column for AND. The OR gate output column is 0 1 1 1.
6OR truth table output: 0 0 0 1 F0 1 1 1
C

Definitions

X = A OR B
D

Fill in the Blanks

Complete each line of code by filling in the missing parts.

1.
X = A __ B
2.
_ = A OR B
3.
A = 1, B = 0 -> X = _
4.
A = 0, B = 0 -> X = _
5.
OR truth table X column: 0 1 1 _
E

Spot the Error

Shade in the letter of the line that contains an error.

Question 1
A Gate: OR
B Inputs: A and B
C Output column: 0 0 0 1
Question 2
A A <- 1
B B <- 2
C X <- A OR B
D OUTPUT X
Question 3
A Gate: OR
B Inputs: A and B
C Output X is 1 if A and B are 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
Question 5
A Expression for OR gate:
B X = A AND B
C Inputs: A and B

Answer Key

The OR gate
Section A: Quick Questions
Q1
A — X is 1 when at least one input is 1
Q2
B — X = A OR B
Q3
A — 0 1 1 1
Q4
A — X = 1
Q5
B — X = 0
Section B: Match the Pairs
Q1
X = A OR B → The output X is 1 when A is 1, when B is 1, or when both are 1.
Q2
A=0, B=0 -> X = 0 → The only input row where an OR gate outputs 0, because neither input is 1.
Q3
The truth table output column for an OR gate with inputs 00, 01, 10, 11 in order → 0 1 1 1
Q4
The OR gate has two inputs called A and B and one output called X → X = A OR B
Q5
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.
Q6
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.
Section C: Definitions
Q1
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.
Section D: Fill in the Blanks
Q1
X = A OR B
Q2
X = A OR B
Q3
A = 1, B = 0 -> X = 1
Q4
A = 0, B = 0 -> X = 0
Q5
OR truth table X column: 0 1 1 1
Section E: Spot the Error
Q1
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.
Q2
B — Logic gate inputs are single bits, so B can only be 0 or 1. The line should be B <- 0.
Q3
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'.
Q4
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.
Q5
B — The expression for the OR gate is X = A OR B. X = A AND B is the expression for the AND gate.