Understanding Basic Electricity
Refer to figure - Fields, for the following discussion.
Electricity is the movement of electrons through a carrier ( conductor ). It's caused by an imbalance in the charge ( from electrons ) between two ends of a conductor. The imbalance is referred to as an electric field ( voltage ) and is measured in volts ( amplitude or strength of the charge ). The movement of electrons through a conductor is referred to as the current and is measured in amperes ( amperage or amps for short ).
The best known conductor of electricity are; copper ( Cu ), silver ( Ag ) and gold ( Au ), basically any metal. The best conductor in general use is gold followed by silver then copper. The most used conductor is copper. Copper is in abundance and has better chemical properties ( less reactive ) than gold or silver. You will note on the periodic table that the best conductors are found in group 11.
It is easy to raise the kinetic energy of the valence electrons of metals to cause them to move from one atom to an adjacent atom ( they hop the short distance between outer sub shells ). It's this property that makes them good conductors of electricity.
An insulator is an extremely poor conductor ( air, glass, paper etc. ).
A battery is a simple source of electrical energy ( power ). A simple battery is composed of two electrodes and a separating electrolyte ( ionic compound ), generally in the form of a paste. The positive electrode ( positive terminal ) is referred to as the anode. The negative electrode ( negative terminal ) is referred to as the cathode. In an electrolyte the positive ions move to the anode and the free electrons move to the cathode.
Refer to figure - Electric Circuits, for the following discussion.
To create an usable electrical current you need to have a power source and a good conductor. The battery and conductor are used to convert chemical energy into electrical energy. The conductor creates an electrical path from the cathode to the anode.
To regulated the amount of current in a conductor, a very weak insulator is used to resist the current flow. Resistance is measured in ohms. Without resistance a short circuit is created and can cause a battery to explode. In general resistance converts electrical energy into thermal ( heat ) energy.
A battery is a type of DC ( direct current ) source. The battery supplies a constant voltage. With a DC source the current flows only in one direction, from the cathode to the anode. In the beginning it was thought that current flowed in the opposite direction and is called conventional current flow.
The basic electrical equation that relates voltage, current and resistance is:
I = V / R
I is the current in amps ( a ). V is the voltage in volts ( v ). R is the resistance in ohms ( ).
1 amp = 1 volt / 1 ohm
1 a = 1 v / 1
In the DC circuits example, circuit 1, resistors 1 and 2 are in series. The same current flows through both resisters. Circuit 1 is in parallel with circuit 2, because they have separate currents produced by the same voltage source. Adding resistor 3 ( circuit 2 ) lowered the resistance seen by the battery.
How do we know?
The battery supplies a constant voltage. The values of R1 and R2 haven't changed, so the current through them is the same. B1 must now supply current to circuit 2. An increase in current with a constant voltage, means a reduction in resistance.
Parallel circuits reduce resistance.
Series circuits increases resistance.
Circuits 1 and 2 are closed circuits, because the same current leaving the cathode enters the anode.
With an AC source the current flows in one direction, then the other. There is no cathode and anode in an AC source. The changing direction of current flow is caused by the polarity of the power source changing.
The AC circuits example shows how electrical energy is transferred through an open circuit ( how all wireless systems work ).
The electric field across a conductor can be picked up by another conductor running parallel to it and will produce a current in the second circuit. This affect is called induction, the second current was induced by the electric field. To get maximum coupling you need to get the two conductors as close as possible ( strength of field ) and parallel to each other for as long as possible ( quantity of field ).
To couple as much electric field as possible between two conductors, a conductor in the form of a wire is wound around a rod ( this is called a coil or inductor ). A second wire is then wound around the same rod on top of the first wire. These two coils form a transformer. Because of the coiling of the wire, there is more wire in a smaller space ( linear inch ), which produces a longer period of time the first wire's electric field is in contact with the second wire, thus transferring more energy to the second circuit.
The electric field across L1 ( called the primary coil ) will be induced across L2 ( called the secondary coil ). The electric field across L2 will cause a current to flow in circuit 2, if circuit 2 is a closed circuit. If circuit 2 is an open circuit, then the electric field across L2 appears between the antenna and ground. The antenna is used to radiate ( transmit ) the electric field. This radiated field will induce an electric field in a another antenna ( receiver or detector ). The detected electric field will produce an electric field across it's primary coil. The primary coil induces an electric field in the secondary coil ( a closed circuit ) which will cause a current to flow in that circuit.
It is possible for a spy outside your house with the right equipment to detect the radiation given off by your monitor to see exactly what is being displayed. This is why in high security buildings, the walls are made of copper ( solid or screened ). The copper, routes radiation from both the inside and outside to ground, preventing electromagnetic eavesdropping.
A power source can also come in the form of a constant current source. With a constant current source the voltage varies with changes in the resistance of a circuit.
What was covered:
Last updated: Mar 4, 2011