LESSON 02 – CIRCUIT DIAGRAMS

 

 

LESSON NOTE

DEFINITIONS

 

circuit: A closed path in which electricity travels.

 

load: A device that consumes electric energy and creates another type of energy (light bulb, resistor, heater, speaker)

           

source: The source of the energy, it contains access to both the positively charged point and the negatively charged point.

 

CIRCUIT SYMBOLS

 

Name

Symbol

Notes (Discussion Only)

Dry Cell / Battery
(1.5 V)

Each 1.5 Volts requires another two vertical lines (one short and one long). This is an example of a SOURCE.

Notice that the negative side of the battery is at a short line.

Current always flows from the negative side to the positive side of the battery.

Dry Cell / Battery
(3 V)

Dry Cell / Battery
(6 V)

Light

A light is a LOAD and uses energy in a circuit.

Resistor

A resistor is also a LOAD because it uses electrical energy. Its purpose is to generally reduce the amount of energy available to other loads in order to protect them.

Switch

A switch (shown open) is neither a load or a source, it simply opens and closes the circuit.

Voltmeter

A voltmeter is used to measure the potential difference between two parts of a circuit. It is ALWAYS placed in parallel (i.e. the electrons do not have to pass through the Voltmeter)

Ammeter

An ammeter is used to measure the current at a specific point in a circuit. It must connected in series (i.e. the electrons have no choice but to pass through it.

Below are a couple of examples of circuit diagrams created using the standard symbols.

 

 

 

TYPES OF CIRCUITS

 

There are three types of circuits:

  • Series circuits
  • Parallel circuits
  • Combination circuits


For now, our focus will be on identifying each type of circuit based on a circuit diagram.

A series circuits contains only a single path with one or more loads on it.  All electrons go through all loads.




A parallel circuit contains multiple paths but each path only has one load.  All electrons go through exactly one load.

 

A combination circuit contains multiple paths with some electrons passing through more than one load.