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Electrical System
Grade 8
AND & OR Logic GatesEdit
There are two types of electrical systems, viz. Digital and Analogue. Digital systems operate on logic circuits. The logic state or logic level of a system can either be HIGH or LOW.
This high and low state is referred to as ON or 1 to represent High and OFF or 0 to represent Low. We use logic gates in electrical systems to decide in a logical way our desired output.
The table is called a truth table. It shows the possible logic levels of the circuit by using a 1 to indicate ON and a 0 to indicate OFF.
This circuit can also be represented as a Systems Diagram as follows:
Activity 1:Edit
Practical, truth table and systems diagram
Practical
Gather the necessary components and connect up the circuit shown below:
Truth Table
Complete the truth table alongside the circuit
This is an AND circuit ­ the lamp will only light up if S1 AND S2 are closed.
Systems Diagram
Draw a systems diagram to represent the AND circuit.
Activity 2:Edit
Practical and truth table
Practical
Gather the necessary components and connect up the circuit shown below:
Truth Table
Complete the truth table below:
S1 
S2 
L1 
0 
0 
0 (off) 
1 
0 

0 
1 

1 
1 

This is known as an OR circuit ­ for the lamp to light up either S1 OR S2 need be closed
Glossary:Edit
Switch: a device which allows or prohibits electricity to flow.
Conductor: a material which allows electricity to flow through it. All metals are conductors.
Circuit diagram: a drawing which uses circuit symbols to represent components.
Truth Table: represents the functioning of a digital circuit. This table uses a `1' to indicate a closed switch (or an `on' lamp, motor etc.), and `0' indicates an open switch (or an `off' lamp, motor etc.).
Logic state or logic level: tell us if the system is high or low or on or off.
Analogue system: has a range of values within its limits
Digital system: have discreet values within its limits
`AND' gate: produces 1 or high when all of its inputs are 1 or high
`OR' gate: produces 1 or high when any of its inputs is 1 or high
Author: Ricardo Miller Contributions by Osman Sadeck Editor: Osman Sadeck