As a phenomenon that has fascinated us for ages, lightening is simply a natural source of electricity. A single bolt of lightening harnesses enough electricity to supply a person's needs for a lifetime. In another form, electricity can be found as the power in a battery that turns the engine to start your car. Electricity is also the force that ignites the gasoline in the car's engine. Despite all its power, electricity is also the method of carrying information from your brain to your muscles, enabling you to move. From lightening bolts to brain waves it is all made up of the same stuff: electrons.
Atoms are the building blocks of nature. They are too small to see and yet the subatomic particles inside the atoms are even smaller. There is a nucleus in the center of each atom, and other particles orbit around the central core. Just as planets orbit the sun, charged particles orbit the nucleus.
There are particles with negative charges and there are particles that have positive charges. An atom's core contains positively charged particles. Electrons, which are negative particles, orbit around the nucleus. There have been more than one hundred different kinds of atoms identified by scientists. An atom's element type is determined by the number of positively and negatively charged particles in the atom. When different atoms combine they can form various materials. For example, a hydrogen atom has one positively charged particle in its nucleus and one electron around the outside. An oxygen atom has eight positive particles in the nucleus and eight electrons around the outside. When two hydrogen atoms combine with one oxygen atom, water is formed.
Charged particles in atoms behave very similar to the poles of magnets. A positively charged particle will attract a negatively charged particle. But two positive or two negative particles repel each other. Just remember that opposites attract.
Electrons always stay near the nucleus of the atom. The positive charge of the nucleus attracts the negative charge of the electrons. Since electrons all have a negative charge, they repel each other, which causes them to spread apart and fill the space around the nucleus. Because atoms have an equal balance of negative and positive charges, the atoms are neutral. These atoms show no electrical effect to the outside world.
It is easy to separate an electron from an atom in many materials, especially metals. When the atom loses one of its electrons the stability and the electrical balance of the atom is upset. Because there is one negative charge gone, the atom has an excess of positive charges. The free electron has a negative charge. The atom that has lost an electron is referred to as a positive ion because of its net positive charge. It takes billions of these similar ions in one place in order for the quantity of charge to become large enough to cause a noticeable effect.
These positively charged ions can pull negative particles, or electrons, from neutral atoms. These electrons are able to move through the space between the atom and the ion and eventually orbit the positively charged ion. This would cause the positively charged ion to become a neutral atom again, forcing the other atom to become a positively charged ion. Once you have a series of these exchanges, with electrons moving from one atom to the next there is a steady flow of electrons. This flow of electrons is called electricity.
Some atoms hold firmly to their electrons and others keep only a loose grip on them and let them slip away easily. This would allow some materials to carry electricity better than others. Materials that keep only a loose grip on their electrons are called conductors. Materials that hold tightly to their electrons are called insulators.
The flow of electricity through a wire is very similar to the flow of water through a pipe. Understanding the concept of what happens when you open a faucet and the water comes out, will help us to explain the flow of electricity and electronics in general.
In water systems, a pump takes water from a large supply and puts it into a storage tank. Then it uses air pressure or the force of gravity to push the water through pipes to the faucets in your home. We can compare the flow of electrons through a wire to the flow of water through a pipe. In both situations we need some force to to exert pressure and make the flow possible.
The amount of pressure needed to push water to your house depends greatly on the path the water has to take. If the path includes flowing over several hills along the path, the force will need to be greater than if it just had to flow down hill. The opposition that electrons must overcome regulates the pressure required to make the electrons flow in an electrical circuit. Electromotive force, or EMF, is the pressure the forces the electrons through a circuit.
EMF is very similar to water pressure. More pressure moves more water just as more EMF moves more electrons. EMF is measured in a unit called the volt (V), so it is often referred to as voltage rather than EMF. Voltage is measured by a device called a voltmeter.
Electric wall outlet in your home = 120 Volts
Outlet for electric stove / dryer = 240 Volts
Car battery = 12 Volts
A single D cell battery = 1.5 Volts
Using metric system prefixes, we can express 1000 volts simply as 1 kilovolt or 1 kV.
Looking at how electrical voltage pushes electrons through a circuit in a slightly different way may help you to understand. Remember that like-charged objects repel. If there is a large group of electrons, the negative charge of these electrons will act to push other electrons through the circuit, just as a large group of positively charged ions will pull electrons through the circuit.
Because there are two types of electric charge (positive and negative), there are also two polarities associated with voltage. All voltage sources have two terminals, or poles: the positive terminal and the negative terminal. The positive terminal attracts electrons and the negative terminal repels electrons. If we connect a piece of wire to the two terminals of a voltage source, electrons will flow through the wire. We call this flow an electrical current.
Remember the pump in our water system? We used it as the source from which to pull water and force it into the pipes. Electrical circuits also require an electron source and a "pump" to move the electrons along. A battery is a good example of a power supply. The battery is used as both the source and the pump. A battery acts like a storage tank in our water system and also like the pump by providing pressure to keep the electrons moving.
At a negative terminal on a power supply there is an excess of electrons, similarly there is an excess of positive ions at the positive terminal. When a wire is connected between the two terminals voltage generated by the power supply causes electrons to move through the wire. Batteries can be found in many different sizes, and is only one kind of voltage source.
Just as the flow of water in a stream of current, the flow of electrons is called electric current. Each electron is extremely small and it takes quintillions and quintillions of electrons to make a toaster heat bread or a tv draw pictures.
As water flows from your home faucet you are not able to count every drop, as the numbers would be very large and unmanageable, not to mention that the drops would be coming out much too fast to count. We cannot easily deal with large numbers of individual electrons either. You need to measure both of these with larger quantities, so with water we use gallons per minute, and with electric current we use amperes. An ammeter is the device used to measure current.
If you could count all the electrons flowing past one point on a piece of wire you would count 6,240,000,000,000,000,000 in one second. This would symbolize one amp of current. When a circuit's current is expressed in amperes, remember that it is a measure of the number of electrons flowing through the circuit. A current of two amperes has twice as many electrons as a current of one ampere. Two amperes is expressed as "2A" or "100 mA" (milliamps) for 0.1 amperes. Current is most often expressed in amps, milliamps, and microamps.
Earlier when we mentioned insulators and conductors we talked about how conductors allow the flow of electrons, while insulators prevent the flow of electrons. Common conductors are silver, copper, steel, aluminum, mercury, zinc, tin, and gold. Common insulators are glass, rubber, plastic, ceramic, mica, wood, and air. Also, pure distilled water is a fairly good insulator, however most tap water is a very good conductor because it has minerals and other impurities dissolved in it.
Think about what would happen if you partially blocked a water pipe with a sponge. Eventually water would get through, but it would have less pressure than before. The sponge resists the water trying to flow through the pipe and it takes pressure to overcome that resistance.
Conductors also present some resistance to the movement of electrons. Resistors are devices that are designed to make use of this resistance. They control the amount of current that flows through a circuit because they resist the flow of electrons.
In our water pipe, increasing the pressure forces more water through the sponge. In our electrical circuit, increasing the voltage will force more current through the resistor. The relationship between voltage, current, and resistance is very predictable. This relationship is called Ohm's Law and it is the most basic electronics principle.
Resistance is measured in a basic unit called the ohm. The abbreviation for ohms is Ω, the Greek capital letter Omega. A resistor having 47 kilohms would be written as 47kΩ and a resistor with 1.2 megohms would be written as 1.2 MΩ. The ohmmeter is the device used to measure the amount of resistance in a circuit.
Ohm's Law tells us the current through a circuit equals the voltage applied to the circuit divided by the circuit resistance. It also states that the circuit resistance is equal to the voltage applied to the circuit divided by the current through the circuit. Finally, it states the voltage applied to a circuit is equal to the current through the circuit times the circuit resistance.
The formulas are as follows:
current = voltage / resistance
resistance = voltage / current
voltage = current * resistance
E = voltage, I = current, R = resistance
When current flowing through a circuit does not follow the path we expect it to, and instead it finds a shorter path between the terminals of the power source, we have a short circuit. When this happens there is less resistance to the flow of electrons so there is a larger current. Often the current through a short circuit is so large that the wires and components cannot handle it and are damaged. A short circuit always draws more current than was intended for the circuit.
The opposite of a short circuit is an open circuit. When current is interrupted, just as it is when you turn a light switch off, you have an open circuit. There is no current through an open circuit. Often this is caused by a switch which opens the circuit, letting a layer of insulating air between the contacts so no current can flow. This break in the current path presents an extremely high resistance. An open circuit can be both good and bad. Turning a circuit on and off by a switch would be an example of a good use for an open circuit. An open circuit can be bad if it is an unwanted condition caused by a broken wire or bad component.
Suppose there is a circuit with two resistors connected so the current goes from the battery, through one resistor, then through the other and finally back to the battery. Knowing how much current flows through the circuit, we can use Ohm's Law to calculate the voltage across each resistor. The voltage that appears across each individual resistor is called a voltage drop.
Voltage drops occur because electrical energy is used up or consumed. In reality, electrical energy is never lost - it is just changed into another form. For example, the resistor heats up because of the current running through it, so in reality resistance converts electrical energy to heat energy. As you can imagine, more current produces more heat and makes the resistor become warmer. It is possible for the current to become so large that the resistor might even burst into flames.
When electrons flow through a light bulb the resistance of the filament converts some electrical energy to heat. In fact, the filament in a bulb gets so hot that it even converts some of the electrical energy to light energy.
We use the term power to define the rate of energy consumption. The basic unit for measuring power is the watt. The unit watt is abbreviated with a W. The higher the amount of wattage the more electrical energy that will be used each minute or hour.
In everything we have talked about until now we have been talking about direct current electricity, known as DC for short. In direct current, the electrons flow from negative to positive. Batteries are the most common source for direct current, but we can also get DC from a solar panel. In our water system analogy, we think of water flowing only in one direction through the pipes, but what is stopping water from actually flowing in either direction?
There is a second kind of electricity called alternating current, or AC. With AC, the terminals of the power supply rapidly change from positive to negative to positive and so forth. Because the terminals are changing and electrons always flow from negative to positive, AC first flows in one direction, then the other. Thus the current alternates in direction.
One complete round trip is called a cycle. The number of complete cycles that occur in one second determines the frequency, which is measured in hertz, abbreviated Hz.
Parts can be connected in two basic ways in an electrical circuit. For example, if we hook several resistors together in a string it forms a series circuit. If we connect several resistors side by side to the same voltage source it forms a parallel circuit.
Thinking back to our water system example, what would happen if we put another sponge along with the first? The second sponge would further reduce the flow. The same task could be accomplished with a single larger sponge. The total resistance in a series circuit is the sum of all the resistances in the circuit.
Now on to the subject of parallel circuits. This would be very similar to having two water pipes running side by side. More water is able to flow through two parallel pipes of the same size than through a single one. With the two pipes the current is greater for a given pressure.
Now imagine these pipes had sponges in them, the flow would be reduced in each pipe. There are still two paths for the water to take and more water will flow then if there was a single pipe with a similar sponge in it. Adding a resistor in parallel with another provides two paths for current to follow. This reduces the total resistance. It is possible to connect more than two resistors in parallel, providing even more paths for the current. This will reduce resistance even more.
R Total = R1 + R2 + R3 + . . . + Rn
where n is the total number of resistors.
In a parallel circuit, things are a bit different. The total resistance of two equal-value resistors connected in parallel is always half the value of one of the resistors.
R = 1
1/R1 + 1/R2 + 1/R3 + . . . + 1/Rn
where n is the total number of resistors.
A magnetic field is created around every wire in which electric current flows. A magnetic field represents the invisible magnetic force, such as the attraction and repulsion between magnets. The magnetic field is positioned in concentric circles around the conductor, like an invisible tube. The field is created when the current flows, and collapses when the current stops. Likewise the field increases in strength when the current increases and decreases as the current decreases. The force generated around a straight piece of wire is usually very small, but if that same wire is formed into a coil the force becomes much greater. This is due to the fact that the magnetic field around each turn also affects the other turns, and together the combined forces produce one large magnetic field. Much of the energy in the magnetic field is concentrated in the material in the center of the coil. Most practical inductors consist of a length of wire wound around an iron core.
An inductor stores energy in a magnetic field, and this property is known as inductance. Magnetic fields have the ability to set electrons in motion. As the magnetic field increases in strength, the voltage on the conductor within that field also increases, and vice versa.
If you apply voltage to an inductor it will establish an electrical current in the inductor and this current will produce a magnetic field. This magnetic field in turn will induce a voltage in the wire. The voltage induced by the magnetic field of the inductor resists the applied voltage, and the inductor will oppose the increase in current. This is the basic property of inductors.
When an AC voltage is applied to an inductor, the current through the inductor will reverse direction every half cycle. This means that the current will be constantly changing and the inductor will oppose this change. Energy is stored in the magnetic field while the current is increasing during the first half cycle. This energy will be returned to the circuit as the current starts to decrease and a new magnetic field will be produced during the second half cycle. The north and south poles of the field will be the reverse of the first half cycle. This process keeps repeating as long as the AC voltage is applied to the inductor.
Inductors have some important roles in electronic circuits. When an AC signal is applied to an inductor the inductance will oppose or reduce the flow of AC. But when the DC signal is applied to an inductor, the inductance will have very little effect on the current, at least after that initial opposition. Inductors reduce the flow of AC signals but allow DC signals to flow freely.
The basic unit of inductance is the henry, abbreviated H. The henry is often too large for practical use in measurements, so we use the millihenry, abbreviated mH, or microhenry, abbreviated µH.
L Total = L1 + L2 + L3 + . . . + Ln
where n is the total number of inductors.
For parallel-connected inductors:
L Total = 1
1/L1 + 1/L2 + 1/L3 + . . . + Ln
where n is the total number of inductors.
A simple capacitor is formed by separating two conductive plates with an insulating material. If you connect one plate to the positive terminal and one plate to the negative terminal of a voltage source, we can build up a surplus of electrons on one plate. Eventually the voltage across the capacitor will be equal to the applied voltage, and the capacitor will be charged. This stored electric charge produces an electric field, which is an invisible electric force of attraction or repulsion. The capacitor stores energy as an electric field between the two plates. Once the capacitor has reached its full charge which is equal to the voltage of the applied signal, no more charge will flow onto the capacitor plates, and the current is stopped.
If we would then connect a load to a charged capacitor it would discharge, releasing the stored energy through the load. Capacitance is the basic property of a capacitor and is the ability to store a charge in an electric field.
If we connect an AC signal to a capacitor, the plates will charge during one part of the AC cycle. After the signal reaches the peak voltage, the charge will start to flow back into the circuit in the opposite direction until the capacitor is charged with the opposite polarity during the second half cycle. This process of charging will continue as long as the AC signal is applied to the capacitor.
Capacitors play a role that is the exact opposite to that of inductors. A capacitor will block direct current because as soon as the capacitor is charged to the applied voltage level, no more current can flow. A capacitor will pass alternating current with little or no opposition, however. The farad is the basic unit of capacitance and is abbreviated F. Like the henry, the farad is usually too large a unit for practical measurement and instead we use microfarads, µF, and picofarads, pF.
C Total = C1 + C2 + C3 + . . . + Cn
where n is the total number of capacitors.
For capacitors in series we use the formula:
C Total = 1
1/C1 + 1/C2 + 1/C3 + . . . + Cn
where n is the total number of capacitors.