Boolean Logic
Overview
Underneath every calculation a computer performs there are switches, and each switch can only be open or closed. Out of that one crude ingredient, arranged with enough care, comes arithmetic. This is not a metaphor. A circuit built from three kinds of gate, none of which knows anything about numbers, can be wired so that it adds two binary digits together and produces the right answer every time, and one such circuit appears on the specimen paper for this qualification.
This lesson gives you the three gates the specification examines, NOT, AND and OR, together with their truth tables. You will build truth tables for circuits made of combinations of them, interpret the results to work out what a circuit is actually for, write a Boolean expression that describes a circuit, and go the other way by designing a circuit that implements an expression. Everything here is small, exact and checkable, which makes it some of the most reliably scoreable content in the whole specification.
Objectives
- Construct truth tables for the following logic gates:
- NOT
- AND
- OR. NOT AND OR Construct truth tables for simple logic circuits.
- Interpret the results of simple truth tables. Create, modify and interpret simple logic circuit diagrams.
- Be able to write a Boolean expression to represent a logic circuit and to draw a logic circuit that implements a Boolean expression.
Mind map
This topic is mapped out so you can see how the ideas connect.
Open the mind map in the app
Lesson Note
Complete Note Available on the Green Bridge App
Get the Green Bridge CBT app on your phone or computer for the complete IGCSE library: past papers, mark schemes, mind maps, flashcards and audio lessons.
Lesson Evaluation
Congratulations on completing the lesson on Boolean Logic. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- Which gate gives an output of 1 only when both of its inputs are 1? A. NOT B. AND C. OR D. None of these Answer: B
- How many rows are needed in a truth table for a logic circuit with three inputs? A. 3 B. 4 C. 6 D. 8 Answer: D
- What is the output of an OR gate when both of its inputs are 0? A. 0 B. 1 C. It depends on the previous input D. The gate has no output Answer: A
- In the notation used by this specification, how is A AND B written? A. A + B B. A with a bar over it C. A and B joined by a dot D. A minus B Answer: C
- A circuit has output Q given by NOT A ANDed with B. What is Q when A = 1 and B = 1? A. 0 B. 1 C. Undefined D. It alternates Answer: A
Work through these questions in the app
Work through these questions in the app
Recommended Books
Practice Mock Questions
Want to practice mock questions on Boolean Logic? Download the Green Bridge CBT app to access mock questions and full practice assessments for this topic.
Download The App On Google Playstore
Everything you need to excel in your exams
