Even though basic electrical theory was not understood until much later, electricity has existed in the world since the beginning of time.
Long before anyone heard the word electricity, people had seen lightning and experienced shocks from electric fish. Written work from the Ancient Egyptians dating back to 2750 BC mentioned a type of fish they called “Thunderer of the Nile”. They believed these fish were to “protect” all of the other fish.
Ancient writings from Pliny the Elder and other naturalists described a numbing effect when shocked by a catfish or a torpedo ray, and realized such a shock could travel along a conductive object.
However, electricity remained mostly a strange phenomenon until 1600, when the English scientist William Gilbert began to study electricity more closely.
Many other scientists, inventors and experimenters became fascinated with electricity and began their own research, which led to our understanding of electricity today.
Every piece of matter is made up of molecules and all molecules are made up of atoms. The elements in all atoms are protons, electrons and neutrons.
The negative charge is carried by electrons, while the positive charge is carried by the protons, and neutrons are naturally neutral. This means that the electric charge depends on how much electrons and protons it contains.
Electrical theory dictates that matter is positively charged if an atom in the matter contains more protons than electrons, and negatively charged if more electrons than protons are present.
Therefore, when considering polarity, how much charge an object has is equal to the total amount of charges of all the atoms. The coulomb (C) is used to measure the electrical charge, where 1 C equals 6.24 x 10^18 electrons or protons.
This calculation comes from Coulomb’s law, which states that the force experienced by two charges placed at a distance is directly proportional to the sum of the multiplied charges, and inversely proportional to the distance.
In order for current to flow there must be a continuous path from the negatively charged source to the positive.
The electric charge moves to create current. How quickly the charge changes in a set amount of time determines the electric current.
This current flows in the opposite direction of the way the electrons flow in the circuit. Because the electrons always flow from low potential to high potential (negative to positive), the electric current flows from positive to negative.
The current will always take the path with the lowest resistance.
How much opposition the conductor or metal wire presents to the electric current flow is the electrical resistance. The lower the resistance, the easier current will flow. Think of current like water flowing through a pipe, if the pipe is small there is more resistance to water flow, if the pipe is large the water will flow much easier. A larger wire size will allow more current to flow.
There are two basic ways in which resistive devices can be hooked up, series and parallel. Loads hooked up in series will affect the circuit current in different ways than in parallel.
Ohm's law was named after Georg Ohm, a German physicist who published a treatise in 1827.
In it, he explained measurements of applied voltage and current by using a simple electrical circuit made with varying lengths of wire.
The law states that electrical current in a circuit or conductor will always be proportionate to the voltage across the conductor or circuit, and inversely proportional to the total resistance.
The e.m.f. (electromotive force) is voltage generated by a source of energy, or by varying the magnetic field, as discovered by Faraday.
Faraday’s Law was developed when he showed that a conductor placed within a magnetic field with time variations, electric current would be induced.
The name – electromotive force – implies this is a force, when in fact the e.m.f. is the energy or potential per unit of charge. This potential is measured in volts.
An electric circuit provides a path for the current to flow to a from a point. The electric current always flows from positive to negative, and takes the path with the least resistance.
An example of this is often seen when someone is working without wearing properly insulated footwear. The worker will experience an electrical shock, because the body offers a path towards the ground with very low resistance.
This means the body has become part of the circuit.
A transistor is mainly used as either an amplifier or a switch. The transistor is made of semiconductor material, and is an important part of the circuit.
The device has three terminals (base, collector and emitter), one of which is used to turn the transistor ON or OFF. Inside there are two junctions of semiconductors.
These are the electrical quantities used to describe basic electrical theory. You will find them in all electrical systems.
Some systems may be more complicated and complex, while others might be very simple, but every one will contain these quantities.
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