Circuit Diagrams
An electrical circuit is made up of a few electrical items that are connected together, so that a current can flow round and round. A simple example is a battery connected to a light bulb by wires.
To understand circuits and to make new circuits, we must often draw pictures of these circuits to help us think. If we need to draw many, it takes a lot of time to draw batteries, light bulbs and other things properly. To make it easy, we always use simple pictures to represent these items. Such pictures are called electrical symbols.
The following are symbols that we often see in circuit diagrams.
Cell - the smallest unit of a battery.
It supplies a direct current.
Battery - a number of cells connected together.
Open switch - A switch is used to connect or disconnect
two wires, in order to switch on and off a circuit.
This picture shows the wires disconnected. This means
current cannot flow. In this case,
the circuit is called an open circuit.
Closed switch - a switch that connects two wires together,
so that current can flow through. In this case, the circuit
is called a closed circuit.
Light dependent resistor (LDR) -
A resistor that has high resistance in the dark, and
low resistance in light.
Temperature dependent resistor (TDR) - A resistor that has high resistance
when cold, and low resistance when hot.
Light bulb - an electrical part that gives out light
when current flows through it.
Ammeter - a device that tells us the value of current
that flows through it.
Voltmeter - a device that tells us the potential
difference between two points.
Magnetising coil - a coil of wire that is used
to magnetise a magnetic material like iron.
Fuse - an electrical part that breaks when the current
is too high.
Relay - a switch that closes (switches on) when
a magnet is near.
Light emitting diode (LED) - a diode that gives out light
when current flows through it.
Diode - a electrical part that allows current to
flow through it in one direction, but not in the other
direction.
a.c. mains - a device that produces an alternating
voltage (that is, one that keeps changing direction).
This picture shows how various parts of an electrical circuit are represented as symbols in a circuit diagram.
