7 - Logic Gates - 2025

• Computing
• Upper Secondary (Key Stage 4)
• GCSE

Guess the topic?

LOGIC GATES

What are they 

Why we need them

and how they work

Name any electronic device you know

All electronics need logic gates to function

Logic Gate

• Are building blocks in a circuit
•  Make decisions 
• Based upon inputs
• Give an output of either ON or OFF

There are three you need to know well.

AND

Output is only ON when all inputs are ON

Can you think of any device/system that needed you to press two buttons at once to make something happen?

OR

Output is ON if ANY input is ON (including multiples)

Can you think or any system where if one of the sensors was triggered, you would want the system do something about it?

NOT

Output will be the opposite to the input (inverts)

Quick Recall - write down the three gates you just learnt

AND gate with two inputs.
Input A = 1, Input B = 0
What is the output?

1. 1
2. 0

AND gate with 3 inputs.
Input A = 1, Input B = 1, Input C = 0
What is the output?

1. 1
2. 0

DEMO and EXPLORE

When instructed

Go to this website

Try:

• Build three simple circuits for each main gate
• Use toggles and lamps for input and outputs

DEMO if required

OR gate with 2 inputs.
Input A = 0, Input B = 0
What is the output?

1. 1
2. 0

OR gate with 3 inputs.
Input A = 0, Input B = 0, Input C = 1
What is the output?

1. 1
2. 0

OR gate with 2 inputs.
Input A = 1, Input B = 1
What is the output?

1. 1
2. 0

Logic Gate Expressions

Output = a AND NOT b

a	b	Output
0	0
1	0
0	1
1	1

Open Logic.ly here

Draw

(a OR b) AND (NOT c)

with logic gates:

(a OR b) AND NOT c

Now, draw the truth table.

(a OR b) AND NOT c

A	B	C	Output
0	0	0
0	0	1
0	1	0
1	0	0
0	1	1
1	0	1
1	1	0
1	1	1

Which Logic gate is this?

1. AND
2. OR
3. NOT

Which Logic gate is this?

1. AND
2. OR
3. NOT

Which Logic gate is this?

1. AND
2. OR
3. NOT

1. 1
2. 0

Research task

Research with google:

NAND gates

NOR gates

XOR gates

Create with logic.ly a drawing using all three of these, and write the truth table for it.