Logic gates and truth tables

Overview

AND, OR and NOT gates and their symbols, truth tables for up to three inputs, conjunction, disjunction and negation, and gates applied to everyday problems.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is a logic gate?

   Model answer

   A logic gate is a component that applies a Boolean operation to one or more binary inputs. A gate gives a single output of 1 or 0.

2. 2

   What does an AND gate do?

   Model answer

   An AND gate outputs 1 only when both of its inputs are 1. Every other combination of inputs gives 0.

3. 3

   What does an OR gate do?

   Model answer

   An OR gate outputs 1 when at least one of its inputs is 1. The output is 0 only when both inputs are 0.

4. 4

   Describe what a NOT gate does.

   Model answer

   A NOT gate takes a single input and outputs the opposite value. An input of 1 gives 0, and an input of 0 gives 1.

5. 5

   How many of the four rows in the truth table for A OR B have an output of 1?

   Model answer

   Three of the four rows output 1. Only the row where A and B are both 0 outputs 0.

6. 6

   What are conjunction, disjunction and negation?

   Model answer

   Conjunction is another name for AND, and disjunction is another name for OR. Negation is another name for NOT.

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