Electric Charge
|
| An electron
is the smallest known particle that can hold an electric charge.
Electrons are part of an atom. Atoms cannot be seen without using
a special instrument known as an electron microscope. At the center
of an atom is the nucleus which is made up of positively charged protons
and neutrons which have no charge. Electrons are negatively charged
and orbit the nucleus. |
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| Elements such
as Copper have 29 atoms, where Hydrogen has just 1. Each element has
different types of atoms; e.g., Copper atoms are different to those
of Hydrogen. |
| All materials
can be classified as having the electrical properties of conductor,
insulator or semiconductor. Copper is a good conductor that shows
little resistance to electron flow. |
| A voltage is always present between two
points with a different number of electrons. Electron flow is greater
in materials that that are good conductors. |
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Conductors, Insulators and Semiconductors
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| Conductors are
mostly metals such as silver, gold, copper and aluminium. A conductor
has less resistance to electron flow than insulators. |
|
| Insulators are
materials that prohibit the flow of electrons unless the voltage is
high enough to break down the insulator and allow electron flow. |
| Semiconductors
are neither conductors or insulators. Silicon is the most common semiconductor.
Semiconductors are treated with a chemical (doped) to give it special
properties. |
| Common Conductors, Insulators
and Semiconductors |
|
Conductor
|
Insulator
|
Insulator Breakdown Voltage
|
Semiconductor |
|
Gold
|
Mica
|
2,000
|
Silicon |
|
Silver
|
Glass
|
900
|
Germanium |
|
Copper
|
Paper
|
500
|
Carbon |
|
Aluminium
|
Rubber
|
275
|
|
|
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Electric Current
|
| Current is the
flow of electrons from a point where there are more electrons to a
point where there are less electrons. For current to flow a voltage
must be present. |
|
| When electricity
was first discovered it was thought that current flowed from positive
to negative. It was later found that electron flow is from negative
where there is an excess of electrons, to positive where there are
less electrons. Today however most electricians refer to current flow
from positive to negative. This is called conventional current
flow. |
| Electric current
is measured in Amps. The symbol is the letter A. In an electric
circuit current does the work and voltage cause the current flow. |
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Electromotive Force
|
|
| The voltage
from a voltage source such as a battery is also known as electromotive
force or EMF. The symbol for EMF is the letter E. |
| Voltage or EMF measured between two points
is also known as electrical pressure. |
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