Year 8 • Computer Systems • Lesson 4

Do Now!

Boolean logic uses statements that are true or false. The operators NOT, AND, and OR help computers make decisions.

Boolean logic overview A visual summary of the NOT, AND and OR operators with small truth-table examples. NOT Flips the answer raining = true not raining = false AND Both must be true keycard = true PIN = true keycard and PIN = true OR At least one is true fruit = false veg = true fruit or veg = true Computers use logic gates to turn true/false rules into real decisions.

Today's Big Idea

Logical operators work on statements that are true or false, and the result is also true or false.

NOT Reverses a statement so true becomes false, and false becomes true.
AND Gives a true result only when both statements are true.
OR Gives a true result when at least one statement is true.

Activity 1: Match the Key Terms

Drag each term into the correct definition.

Boolean logic
Logical operator
Statement
NOT
AND
OR
Term Definition
A way of representing logic and reasoning using true and false values.
A symbol or word that combines or changes true/false statements.
A sentence that can be judged as either true or false.
The operator that flips a statement so the opposite value is produced.
The operator that is true only when both input statements are true.
The operator that is true when at least one input statement is true.

Activity 2: Sort the Statements

Place each example into the operator it matches best.

The statement is true when it is not raining.
A door opens only if the keycard and PIN are both correct.
A game starts when player one or player two presses begin.
A signal becomes true when the switch is not on.
The alarm sounds when motion and activation are both true.
The gate opens if the button on the left or right is pressed.
A result is true when at least one of two statements is true.
The output is false unless both inputs are true.

NOT

AND

OR

Activity 3: Explain the Logic

Use Boolean logic to explain how these two systems make decisions.

A school door unlocks only when a student has a valid keycard and enters the correct PIN. A playground gate opens if the left button or the right button is pressed. Write a short explanation using the words NOT, AND, OR, true, and false.

Start by naming the operator that matches each system. Then explain what has to be true for the output to happen. Use sentence starters like: "The first system uses...", "This is true when...", and "If one input is false, then...". Add one final sentence to show what NOT does to a true or false value.

Download PDF Evidence

Create a record of your starter activity responses.