Electrical engineering is concerned with making use of electricity as a way of transmitting and using power. There are natural sources of electrical power, such as lightning and some living creatures, such as the electric eel, but the main concern of electrical engineering is directed to man-made systems that generate, distribute, and use electricity. Our main uses of electricity depend on converting electrical power to other forms, mainly into mechanical effort, heat and light. These other forms are also our main sources of electrical power.

The first electrical effects to be discovered were those of static electricity, observed when amber was rubbed with silk. The ancient Greeks first discovered these effects, and because amber is called electron in Greek, we have coined the words such as electricity and electronics that are so familiar today. Considerably later, in the eighteenth century, experimenters discovered other effects that also seemed to be electrical, but these were entirely different. Typically, these effects use a chemical action to generate what we now call electric current in a closed path that we call a circuit. As an aid to imagining what was happening, electric current can be compared to the flow of water in pipes.

Think for a moment about a water circuit, such as is used in central heating. The path for the water is closed (Figure 1.1) and the water is moved by using a pump. No water is lost from the circuit and none is added. Turning off a tap at the tank (breaking the circuit) would make the water level rise, because of the pressure of the pump, in the vertical (overflow) piece of pipe. The pump maintains the pressure that makes the water move, and we can use this movement to transmit power because the flowing water can turn a turbine wheel at some other part of the circuit. Hydraulic machines depend on this idea of a liquid in a circuit, though the modern development of hydraulics came later than our use of electricity.

It is not surprising, then, that early experimenters thought that electricity was some kind of invisible liquid. Static electricity effects were explained as being caused by the pressure of this liquid, and current electricity by the flow of the liquid. Electrical engineering is mainly concerned with flow, but the later science of electronics has been based as much on static electricity as on current flow, because we now know much more about what is flowing and why it can flow so easily in metal wires. The fundamental quantity of electricity is electrical charge, and that is what moves in a circuit.

That definition does not tell you much unless you know something about electric charge. No-one knows precisely what charge is (though we are slowly getting there), but we do know a lot about what charge does, and what we know about what charge does is knowledge that has been accumulated since the time of the ancient Greeks. We can summarize what charge does (the properties of charge): What we know about the way that charge behaves has led to finding out more about what it is, and we know now that charge is one of the most important effects in the Universe. Like gravity, charge is a way of distorting space, so that it appears to cause force effects at a distance from the cause of the charge. What we call charge is the effect of splitting atoms, separating small particles called electrons from the rest of each atom. Each electron is negatively charged, and the amount of charge is the same for each electron. The other main part of an atom, the nucleus, carries exactly as much positive charge as the electrons around it carry negative charge (Figure 1.2), if we picture the atom as looking like the sun and its planets. For example, if there are six electrons then the nucleus must carry six units of positive charge, exactly balancing the total negative charge on the electrons.

When an electron has become separated from the atom that it belongs to, the attraction between the electron and its atom is, for such tiny particles, enormous, and all the effects that we lump together as electricity, ranging from lightning to batteries, are caused by these force effects of charge. The forces between charges that are at rest are responsible for the effects that used to be called static electricity (or electrostatics), and these effects are important because they are used in several types of electronics devices.

Another option for an electron that has become separated from an atom is to find another atom that has lost its electron (and is therefore positively charged). The movement of electrons from one atom to another causes a large number of measurable effects such as electric current, magnetism, and chemical actions like electroplating. Of these, the most important for electronics purposes are electric current, and one of its effects, magnetism. Materials that allow electrons to move through them are called conductors; materials that do not allow electrons to move easily through them are called insulators.

The movement of electrons that we call electric current takes place in a circuit, a closed path for electrons that has been created using conducting material. All circuits for current are closed circuits, meaning that electrons will move from a generator through the circuit and back to the generator again. This is essential because unless electrons moved in a closed path like this many atoms would be left without electrons, and that condition could not exist for long because of the large forces that draw the electrons back to the atoms.

These are formal definitions. We cannot easily count the number of electrons that carry charge along a wire, and we cannot easily measure how much work is done when a charge moves. We can, however, measure these quantities by making use of the effects that they cause. Current along a wire, for example, will cause a force on a magnet, and we can measure that force. The voltage caused by some separated charges can be measured by the amount of current that will flow when the charges are allowed to move. The unit of current is called an ampere or amp, and the unit of voltage is a volt. These terms come from the names of the pioneers Ampere and Volta, and the abbreviations are A and V, respectively.

All substances contain electrons, which we can think of as being the outer layer of each atom. Some materials are made out of atoms that hold their electrons tightly, and when electrons are moved out of place it is not easy for them to return to their positions. In addition, other electrons cannot move from their own atoms to take up empty places on other atoms. We call these materials insulators, and they are used to prevent electric current from flowing. In addition, insulators can be charged and will remain charged for some time.

A good example is the party balloon which is charged by rubbing it against a woolen sweater and which will cling to the wall or the ceiling until its charge is neutralized. Surprisingly high voltages can be generated in this way on insulators, typically several kilovolts (kV), where kilo means one-thousand. For example, 5 kV means five-thousand volts. A very small current can discharge such materials, and we use the units microamp (μA), meaning a millionth of an amp, nanoamp (nA), meaning a thousandth of a millionth of an amp, and picoamp (pA), meaning a millionth of a millionth of an amp. There is an even smaller unit, the femtoamp (fA), one-thousandth of a picoamp.

Now let's look at electricity with lower voltages and higher currents. This is the form of electricity that we are most familiar with and which we use daily.

There are several ways of generating a steady voltage, but only two are important for everyday purposes. Batteries are the most familiar method, and the invention of the first battery by Alessandro Volta in 1799 made it possible for the first time to study comparatively large electric currents at voltage levels from 3 V to several hundred volts. A battery is, strictly speaking, a stack of cells, with each cell (Figure 1.3) converting chemical action into electrical voltage. In the course of this, a metal is dissolved into a metal-salt, releasing energy in the form of electrical voltage that can make current flow.

For centuries the zinc–carbon type of cell, and a few others, were the only types known, but in the later twentieth century several other types were discovered. One of these, the lithium-ion (often abbreviated to L-ion), is totally different in construction and delivers more than 3 V, unlike other types that provide a maximum of 1.5 V. Just to confuse matters, there is also a lithium cell ( not lithium-ion) that provides just 1.5 V but has a much longer useful life than the older types.

Some types of cell, such as Li-ion and nickel–metal hydride (NiMH), are rechargeable, so that you can connect them to a (higher) voltage and convert the metal-salt back to the metal – but you need to use more energy than you got out of the cell. As always, no energy is ever created. If anyone ever tries to sell you a motor that runs on air, magnetism, or moonbeams, always ask where the energy comes from (usually it is from the people who have been cheated along the way). You can always detect a charlatan by the way that he or she uses spoof-science phrases like tapping into our natural energy field (and they usually bring crystals into their vaporings as well).

Another way of generating a steady voltage was discovered by Michael Faraday in 1817. He demonstrated the first dynamo, which worked by rotating a metal disk between the poles of a magnet, using the energy of whatever was turning the disk (Faraday's hand first of all, and later a steam engine) converted into electrical voltage that could provide current (Figure 1.4). Strictly speaking, a voltage that is the result of a generator or a battery should be called an electromotive force (EMF), but this name is slightly old-fashioned nowadays.

In these pioneering days, steady (or direct) voltage was the only type that was thought to be useful. A steady voltage will cause a steady current to flow when there is a path of conducting material, a circuit, between the points where the voltage (the EMF) exists. We call these points terminals. A cell or a simple dynamo will have two terminals, one that we call positive and the other negative. When a wire, or any other conductor, is used to connect the terminals, a current will flow, and if the voltage is steady, then the current also will be steady. That does not mean that it will be steady for ever. A cell will be exhausted when its metal is all dissolved, and the voltage will fall to zero. A dynamo will generate a voltage only for as long as the shaft is turned. By convention, we say that the current flows from the positive terminal to the negative terminal (even though we know now that the electrons move in the opposite direction).

A steady voltage will cause a steady current, called direct current ( DC), to flow, and in 1826 Georg Simeon Ohm found what determined how much current would flow. He called this quantity resistance. The three quantities, voltage, current, and resistance, are therefore related, and the unit of resistance is called the ohm in his honor. For any part of a circuit, we can measure the voltage across the circuit (between one end and the other) and the current through the circuit and so find the resistance.

We can determine whether or not a conducting material obeys Ohm's law by plotting a graph of current against voltage, using a circuit as in Figure 1.5(a). If this results in a graph that is a straight line (Figure 1.5b), then the material obeys Ohm's law; it is ohmic. Most metals behave like this if their temperature is kept constant. If the graph is curved (Figure 1.5c) the material is not ohmic, and this type of behavior is found when metals change temperature considerably or when we use semiconducting materials in the circuit.

Power is the rate of doing work, meaning the amount of work done per second. When we use electricity, perhaps for heating, lighting, running a motor, or plating gold on to a base metal, we are making use of power, converting it from the electrical form to other forms. The amount of power that is dissipated or converted can be calculated easily for anything that uses steady voltage and current; it is equal to the figure of volts multiplied by the figure of current. When this power is converted into heat we often call it dissipation because we cannot contain it; it leaks away. The calculation of power, in symbols, is: where V is in volts and I is in amps. The unit of power is the watt, abbreviation W. As an example, if the torch bulb is rated at 3 V 0.5 A then its power is 1.5 W.

Things are not so simple when we are working with quantities that are not steady, but we can always find the amount of power by making measurements of volts and amps and carrying out a multiplication. The difference is that for changing voltages and currents we need to multiply by another factor as well; we will look at that later when we deal with RMS quantities and phase angles.

The voltage (EMF) that is generated by a cell or battery is truly steady, but the voltage from a rotating generator is not. When one side of the revolving coil of wire is approaching a pole of the magnet, the changing voltage is in one direction, but as the wire moves away from the magnetic pole, the changing voltage is in the other direction. Because there are two poles to a magnet, the voltage from a rotating coil rises and falls twice in a revolution, positive for half the time and negative for the other half. This is an alternating voltage, alternately in one direction and then the other direction. The graph looks like that of Figure 1.6 and the time it takes to go through one complete cycle of the waveshape is the time that it takes to turn the coil through a complete revolution. The snake shape of the graph gives rise to the name sinewave, from the Latin word for ‘snake’.

Faraday's later type of dynamo got around this reversal of current by using a mechanical switch called a commutator, which reversed the connections to the coil twice on each revolution, just as the voltage passed through zero (Figure 1.7). This generated an EMF which, though not exactly steady, was at least always in the same direction, so that it was possible to label one terminal as plus and the other as minus. If the shaft of the dynamo is spun quickly enough, there is in practice very little difference between the voltage from the dynamo and the same amount of voltage from a battery. For tasks like heating, lighting, electroplating, battery charging, and so on, the supplies are equivalent.

There are other ways of generating electricity from heat and from light, but they suffer the problems of inefficient conversion (not much electrical energy out for a lot of heat energy in) or low density of energy (for example, you have to cover a lot of ground with light cells to generate electricity for a house). A few small generators use nuclear power directly, by collecting the electrons that radioactive materials give out, but large-scale nuclear reactors use the heat of the reaction to generate steam and supply it to turbines. These are therefore steam-powered generators, and the only difference is in how the steam is obtained (and the hysteria that is generated).

The same is true of the places on Earth where steam can be obtained from holes in the ground, providing geothermal power, but this steam-power is less controllable and certainly not available everywhere. Higher efficiency figures can be obtained where heat is not involved, such as in hydroelectric generators. Wind turbines, in contrast, require the variable voltage that they generate to be turned into a constant voltage and frequency (see later) and these conversions reduce the already low efficiency. If we were really serious about spending money wisely we would try to develop tidal or wave generators that would serve the additional function of protecting our coasts from erosion.

If we omit the commutator of a dynamo and connect to the ends of the coil rotating at a steady number of revolutions per second, the graph of the voltage, plotted against time, shows a shape that is a sinewave, as was illustrated in Figure 1.6. The connection to the coil can be made using slip-rings (Figure 1.8), so as to avoid twisting the connecting wires. This voltage is analternating voltage and when we use an alternating voltage in a circuit, the current that flows is alternating current ( AC). A graph of current plotted against time is of the same shape as the graph of voltage, and the peak of current is at exactly the same time as the peak of voltage in each direction if the circuit contains only resistances.

We can use AC for electrical heating, for electric light, for motors, and in fact for most domestic uses of electricity. It cannot be used for electroplating or battery charging, however, and it cannot be used for most types of electronic equipment. In the nineteenth century, when electronics was in its infancy, the advantages of AC greatly outweighed any minor disadvantages, particularly since AC could be converted to DC if DC were essential. What are the advantages of using AC?

Virtually every country in the world therefore generates and distributes electricity as AC, and the convention is to use a rate of 50 cycles per second (50 hertz or Hz) in Europe or 60 cycles per second (60 Hz) in the USA. In terms of a simple generator, this corresponds to spinning the shaft of the generator at 3000 revolutions per minute (r.p.m.) for 50 Hz, or 3600 r.p.m. for 60 Hz. The abbreviation Hz is for hertz, the unit of one cycle of alternation per second. This was named after Heinrich Hertz, who discovered radio waves in 1884.

Atoms such as those of metals can be so tightly packed together that they can share electrons, and the loss of an electron from a set of these packed atoms does not cause such a large upset in any one atom. In these materials, electric current can flow by shifting electrons from one set of atoms to the next. We call these materials conductors. All metals contain closely packed atoms, and so all metals are conductors, some much better than others. A small voltage, perhaps 1.5 V, 6 V, 12 V or so, can push electrons through a piece of metal, and large currents can flow. These currents might be of several amps, or for very low voltages perhaps smaller amounts (see earlier) measured in milliamps (mA), microamps (μA), picoamps (pA), or even femtoamps.

As well as being closely packed, the atoms of a metal are usually arranged in a pattern, a crystal. These patterns often contain gaps in the electron arrangement, called holes, and these holes can also move from one part of the crystal to another (though they cannot exist beyond the crystal). Because a hole in a crystal behaves like a positive charge, movement of holes also amounts to electric current, and in most metals when electric current flows, part of the current is due to hole movement and the rest to electron movement.

There are some materials for which the relative amount of electrons and holes can be adjusted. The materials we call semiconductors (typically silicon) can have tiny amounts of other materials added to the pure metal crystals during the refining process; this action is called doping. The result is that we can create a material that conducts mainly by hole movement (a P-type semiconductor) or one that conducts mainly by electron movement (an N-type semiconductor). In addition, the number of particles that are free to move (free particles) is less than in a metal, so that the movement of the particles is faster (for the same amount of current) than it is in metals, and the movement can be affected by the presence of charges (which attract or repel the electrons or holes and so interfere with movement). The movement can also be affected by magnets. Semiconductors are important because they allow us to control the movement of electrons and holes in crystals.

AC would be important enough even if it only provided a way to generate and distribute electrical power, but it has even greater importance. A hint of this came in 1873 when James Clerk Maxwell published a book containing equations that showed that an alternating voltage could generate waves of voltage and magnetism in space, and that these waves would travel at the same speed as light. He called these waves electromagnetic waves, and from there it was a short step to show that light was just one of these waves.

Why just one? These waves differ from each other in two ways. One is the number of waves that pass a fixed point per second, called the frequency of the waves. The other is the amplitude (the amount of rise and fall in each wave) (Figure 1.9). Amplitude determines the energy of the wave, so that a large amplitude of a light wave means a bright light. Frequency affects how easily a wave is launched into space and how we detect it.

The range from 300 MHz to 1000 MHz is ultra-high frequency (UHF), used for television transmissions, and once we get to using the unit of GHz (1 gigahertz is equal to 1000 MHz) then the signals are in the microwave ranges, used for mobile phones, satellite communications, and radar. These names are only rough indications of a range, and because we have found it necessary to use higher and higher frequencies over the years we have had to invent names for new ranges of frequencies that we once thought were unusable.

One lower frequency range is particularly significant to us, and is called the audio range. This is the range of frequencies between about 30 Hz and 20 kHz, and its significance is that this is the range of frequencies of sound waves that we can hear (bats might have a different definition). A microphone, for example, used in a concert hall would provide an electrical output that would consist of waves in this range. For speech, we make use of a much smaller range, about 100–400 Hz.

All the electronic methods that we know for generating waves are subject to some limitation at the highest frequencies, and methods other than electronic methods of generating and detecting waves have to be used. At around 1000 GHz, the waves are called infrared, and their effect on us (and any other objects) is a heating effect on all materials that absorb the waves, so that we can detect these waves coming from any warm object. We can also use electronic transducers to convert infrared signals into electrical signals. Higher frequencies, to about 100,000 GHz, correspond to the infrared radiation from red-hot objects, and one small range of frequencies between 100,000 and 1,000,000 GHz is what we call light. Higher still we have X-rays, gamma rays and others which we find very difficult to detect and cannot generate for ourselves.

As far as electronics is concerned, we make most use of the waves in the range from a few hertz to several tens of gigahertz, and radio technology is concerned with how these waves are generated, used to carry information, launched, and detected. Radio, in this respect, includes television and cellular telephones, because the use of the waves is the same; only the information is different.

The waveform of a wave is its shape, and because an electromagnetic wave is invisible the shape we refer to is the shape of the graph of (usually) voltage plotted against time. The instrument called the oscilloscope (see Chapter 17) will display waveforms; we do not need to draw graphs from voltage and time readings. We are seldom particularly interested in the shape of the waves that are transmitted through space, and waveforms are of interest mainly for waves that are transmitted along wires and other conductors in electronic circuits.

The simplest type of waveform is the shape of the wave that is generated by the magnet and coil arrangement that Faraday used (which was illustrated in Figure 1.6). The shape that this generates is called a sinewave (or sine wave) and it is the same shape as a graph of the sine of an angle plotted against the angle. What makes the sinewave particularly important is that any other shape of wave can be created by mixing sinewaves of different frequencies, and any shape of wave can be analyzed in terms of a mixture of sinewaves.

Though a pure sinewave is the simplest wave, its uses are confined to AC power generation and to radio transmitters. Most of the waves that we use in electronics are a long way from a sinewave shape, and one special type, the pulse, has become particularly important from the second half of the twentieth century onwards.

Take a look at the two shapes in Figure 1.10. Wave (a) is called a square wave, for obvious reasons, and it is used particularly when a wave is used for precise timing. Because the edges of the wave are sharp, each can be used for starting or stopping an action. If you used a sinewave there would be some uncertainty about where to start or stop, but the steep edge of the square wave makes the timing action much more certain. For example, the time needed to change the voltage level of such a wave might be only 50 nanoseconds or less (1 nanosecond is a thousandth of a millionth of a second).

The square wave is nothing like a sinewave, and it can be generated naturally by switching a steady voltage on and off rather than by any type of rotating generator. Very precise square waves are generated by electronic circuits that use a vibrating quartz crystal to control the frequency, and these circuits are used in clocks and watches. Even greater precision is obtained from the atomic clock that uses the natural vibration of atoms as a fixed frequency.

The other wave, in Figure 1.10(b), is called a sweep in the USA or a sawtooth in the UK. It features a long, even, rise (or fall) followed by a fast return to the starting voltage. Before 1936, a wave of this shape would have been an academic curiosity, but this is the shape of wave that is needed for a cathode ray tube, for television, or for radar, and we will look at it again in Chapter 8 and Chapter 17. The sawtooth is also an important waveform that is used in electronic measuring instruments.

What marks these waves out as totally different from the sinewave is that they show very sharp changes of voltage. A sinewave never changes abruptly; its rate of change is fixed by its frequency and amplitude. These square and sawtooth waves can change in a time that bears no relation to the frequency or the amplitude. A square wave might have a frequency of only 1 Hz, but change voltage in less than one-millionth of a second (a microsecond, written as 1 μs).

The pulse is a waveform, but one that you might not recognize as a wave because the time of the pulse is very short compared to the time between pulses. Figure 1.11 illustrates three different pulse shapes, all of which share a very sharply rising portion, the leading edge. For a negative pulse, this leading edge would be a sharp fall in voltage.

For example, a pulse might repeat at a rate of 1 kHz, 1000 pulses per second. The actual pulse might have a duration, a pulse time, of only 10 μs, so that the change in voltage lasts only for 10 μs in the 1 ms (millisecond) between pulses. That makes the time of the pulse (its duty cycle) 1/100 of the time between pulses, and these are fairly typical figures. Pulses are used for timing, and they have the advantage that they use very little energy because the change in voltage is so short. A pulse can be used to start an action, to stop an action, or to maintain an action (such as keeping a wave in step, synchronized, with the pulses).

Modern digital electronics systems, particularly computers, rely heavily on the use of pulses, and when we work on these systems we are not greatly concerned about waveshapes, only about pulse timing. There are many things that can change a waveshape, making it very difficult to preserve the shape of a wave. By contrast, it is more difficult to upset pulse timing by any natural means, so that circuits which depend on pulse timing are more reliable in this respect than circuits that depend on waveshapes.

The classic example is sound recording. Hi-fi systems in the past tried to work with a waveform that had a very small amplitude (the output from a gramophone pickup) and keep the shape of the waveform in the form of a copy that had a much larger amplitude. This large-scale copy was used to operate loudspeakers, and we called the whole exercise amplification.

The problem with this system is that a copy of the waveform is never perfect, something that is even more obvious when you make a copy of a copy. Any blemish on the surface of the record, any false movement of the stylus, any interfering signals in the circuits all will make the copied waveform inaccurate, a process we call distortion.

Nowadays the sound is recorded digitally as a set of pulses, using the pulses to represent numbers, and each point in a waveform is represented by a number. Using pulses for counting, we can ensure that the numbers are not changed, so that when the stream of numbers is converted back to a wave, the shape of the wave is exactly the same as was recorded. This is the basis of compact discs, the most familiar of the digital systems that have over the last few years replaced so many of the electronics methods that we grew up with. There will be more of all that in Chapter 11 and Chapter 12.