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NUE 052 - Electrical Characteristics of Materials

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. An atom showing the nucleus and electrons
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.
Conductors, Insulators and Semiconductors
Conductors are mostly metals such as silver, gold, copper and aluminium. A conductor has less resistance to electron flow than insulators.
Cable uses both conductors & 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



 Insulator Breakdown Voltage

















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.
Electric current
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.  
Electromotive Force
A battery is a source of EMF
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.
Practice Tests Practice tests are available on the Practice Test page

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