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It all begins here
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Electric Current - When electrons are moved continuously in a constant direction through a wire we have an electric current. Two important considerations of electric current are the direction of the flow and the quantity of electricity that is transported in a time period of one second. |
Conductors: Based upon the atomic makeup of matter (remember those Jr. High science classes?) and the electrical makeup of the atom, all things are made of electricity. Yet all materials are not equally good as paths for electric current. Those materials that do allow a practical amount of electric current to flow are called conductors. Most conductors are metallic. The factor that makes metal able to conduct an electric current is the abundance of free electrons in the material, the free electrons being electricity that is available to be moved through the metal when the material is part of a complete electrical circuit.. Silver, copper, and aluminum are excellent conductors... while nichrome is a special alloy made specifically to perform as an inferior conductor.... it is often the material a heating coil in a toaster is made of....
Insulators: a group of materials that provide extremely poor paths for electric currents under all normal conditions. The material contains very few free electrons so a practical and useful amount of electric current cannot flow under normal conditions. Examples include: glass, plastic, rubber, mica, ceramic, among others. Another word for an insulator is dielectric. If a material is used as a covering around wires that carry electric current, it is called insulation.
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Some ways in which insulators are used in radio |
Ok, so what makes the random motion of free electrons in a conductor move in a controlled way that is "electric current"? Electrical pressure needs to be applied to the circuit.... this pressure is known as Electromotive force. A source of EMF must have the ability to free electrons from atoms. A cell or battery is an example of a source of electromotive force. There of course many others...
As long as a battery is "good" the separating action removing the electrons from the atoms takes place. This results in accumulating free electrons on the negative terminal (-) and atoms that are missing electrons on the positive terminal (+). Now the free electrons are attracted to the atoms that are missing electrons (remember unlike charges attract?) , but they cannot get together because there is no path inside the battery. However, if we provide some sort of electrical path outside the battery, say a conductor such as a wire connected between the negative and positive terminals, electrons will move along the path in the direction from negative to positive. The directional factor mentioned here is called polarity.
The electrical force that acts on the electrons at the negative terminal... pushing them toward the positive terminal is known as the electromotive force and is developed by the chemical action in the battery.
The Volt: Electrical pressure or electromotive force is measured in units called volts. The difference in potential between two points in an electrical system can also be identified in terms of volts. Voltage output is often what is referred to when a reference is made to voltage. So a flashlight battery cell is 1.5 volts... it has developed an electromotive force of 1.5 volts.
The voltages one encounters in antique radios vary greatly....from millivolts to several hundred volts.
Key Terms On This Page... Use this as a review:
| Electric Current | Conductor | Insulator | Insulation | Dielectric |
| Electromotive Force | Free Electrons | Volt | Battery | |
| millivolt | Positive Terminal | Polarity | µV | Kilovolt |
Once you've mastered this page, go on to "Electric Current"
