Download Electrical energy flows around a path called a “circuit”

S2 Curriculum for Excellence
may 2012
Electricity Summary
Egyptian scientists are thought to have been the first to invent batteries or “cells” using
jars containing a pair of different metal “electrodes” and soaked in acidic liquid
“electrolyte”.
The technique was re-discovered around 2 hundred years ago by an Italian scientist
Alessandro Volta.
A battery, or other “voltage” supply, provides the energy for electrically charged
electrons to carry around a circuit. The bigger the voltage the more energy that is carried
around the circuit and any bulbs in the circuit will get brighter, motors will run faster.
.
There are two types of electric circuit: “series” and “parallel”.
A series circuit allows the electrical energy to flow along a single path.
+ Voltage supply
Resistor
lamp / bulb
The energy is measured by a device called a “voltmeter”.
The voltmeter is not part of the circuit and is connected across the components.
+ 10 Volts 6 V + 4 V = 10 V
6V
4V
The voltage is measured in units called “Volts” or smaller units called “milliVolts”.
There are 1000 milliVolts in 1.0 Volt.
The voltages in the circuit must always add up to the voltage of the supply.
(All the fractions must add up to the whole.)
When more bulbs are added to a series circuit the current decreases and the bulbs
get dimmer.
The energy is carried by an electric “current” measured in units called “Amps” or
smaller units called “milliAmps”. Current is measured using a device called an
“Ammeter”.
S2 Curriculum for Excellence
may 2012
In a series circuit the current has only one path so the size of the current is the same at all
positions. If the series circuit is broken at any point the current stops and drops to
zero.
A “parallel” circuit allows the energy (carried by the electric charges) to flow along
more than one path.
+
switches
In a parallel circuit, with more than path, when the current stops flowing along one path
it can still flow along the other path(s).
The ammeter is part of the circuit. Whatever flows through the wires also flows through
the ammeter.
5mA
2mA
2 mA + 3 mA = 5 mA
3mA
When more bulbs are added to a parallel circuit the current increases and the bulbs
get brighter.
Most household applainces such as microwave ovens, cookers, food mixers etc are
operated by two switches in series; one at the wall socket and one at the appliance.
Most household lighting circuits are connected in parallel. If one part of the circuit is
OFF the other parts can still be ON.