ABOUT THE CLASSROOM: Over time, this column will enhance your understanding of electricity and electronics at a foundation level. The aim of the Classroom is both to educate and empower educators. Topics will be explored with a broad audience in mind; however, links will be made – where possible – to curriculums for high school, primary, and even early childhood. The ACARA curriculum will be used as a reference point, since all states (except for New South Wales) have adopted it, and New South Wales is in the process of syllabus review. Some topics will not be linked to syllabus at all, making it ideal for non-educators; while others will be directly linked, intended for educators. Regardless, each article will provide value and interest for all readers. If you have advanced knowledge, you may find some topics appear slightly incorrect or incomplete; however, this will usually be a result of the simplification process. Where possible, educational terminology and jargon will be avoided; except in those cases where a paragraph can be reduced to a sentence by using it. In this and all other instances, the point being made will be most relevant to educators – be they teachers, tutors, or home-schooling parents. If others are inspired to learn more, there is a lot of reading available on modern teaching and schooling. Commonly used terms, such as ‘scaffolding’, will feature prominently in any reading you may wish to do.
Without electricity, just about everything in our modern lives wouldn't exist. But what is this miraculous and mysterious thing?
The most fundamental concept to embrace when learning electronics is the operation of electricity itself. This starts at the atomic level; however, only a basic understanding of atoms is required, so the depth of learning can be age-adjusted.
All matter in the universe is made up of tiny particles called atoms. They, in turn, are made up of protons, neutrons, and electrons; all except for hydrogen in its most common form. Protons don't serve alot of purpose in electronics, so we won't discuss them too much.Electrons fly around the nucleus in an orbit, similar to the way the moon orbits the earth .
Neutrons are the biggest particle and are made up of a proton with an electron bonded to it. Electrons are the smallest particle, and they are attracted to protons – the middle sized particle – but never bond to them; instead they spin around the nucleus. Electrons will jump from one atom to another, as attracted from a negative charge to a positive charge. An atom with more electrons than protons is an ion that has a negative charge. An atom with less electrons than protons is an ion that has a positive charge. Nature says "Share!" .
It is the movement of these electrons that make up the flow of electricity. However, electrons do not just disappear, nor can the atom exist without them, so electrons must flow from one atom to the next in a circle of some sort. When an external force is applied, such as happens when a battery is attached to a conductor, the electrons are attracted to the positive of the battery, and the negative provided electrons to the circuit .
An electric circuit is like a car racing circuit, during a race. The cars, like electrons, go around and around the circuit, all at about the same speed, lap after lap. An observer may stand anywhere around the circuit to count the cars passing by. Assuming all of the cars finish the race any observer will count the same number of cars (or electrons). Then we can say that the current (number of electrons) counted at any point on the circuit, will always remain the same.
A very large and complex circuit conveys electrical power from a power station where it is generated, through many interconnected circuits, to your home, down to individual appliances, and inside to individual components, the intended load. Even loads can be quite complex, with a computer being as complex as the circuit that brought the electricity to it. Mains electrical power is a different form of electricity, in that the electrons travel back and forth, changing directions 100 times a second, therefore being known as Alternating Current, or 'AC' for short. The study of AC electrical power is mostly undertaken by licensed electricians and engineers. .
Newton stated that every mass will remain in its present state until acted upon by an external force. Even electrons need to be acted on by a force to move. In physics, a fundamental rule is the law of conservation of energy, which states that energy cannot be made or destroyed, only converted from one form to another. Electrons acted on by a force transfer this energy, rather than being the energy themselves.
This may be chemical potential energy stored in a battery, or kinetic energy, such as the motion of a generator spinning. In either case, the energy is transferred to the electrons, which flow along conductors (these will be discussed later), before eventually returning to the source without this energy, having done work along the way.
Along the way, more energy is converted to heat, meaning not all of the output of a power device, such as a battery or generator, is used as electrical energy.
‘Work’ is another physics concept that is slightly beyond the scope of this article. This transfer of energy into work is why a battery goes flat, and why a generator needs to be spun by the constant input of energy such as steam. This chain is another example of the law of conservation of energy.
In many power stations in Australia, burning coal heats boilers. This transfers energy from chemical potential energy to heat energy, stored as pressurised steam. This pressure is piped to turbines, which turn the potential energy of the pressurised steam into kinetic energy by spinning. Turbines are connected to generators, which rotate a magnet around inside a wire coil .
Magnetic fields are one of the things that can cause electrons to jump from one atom to the next, thus chemical potential energy from coal has been transferred to electron flow in a wire.
Of course, there is an efficiency problem with mechanical systems due to friction and lost heat. Only a certain amount of the heat from a boiler will be transferred to steam pressure. Only a certain amount of that potential energy is transferred to kinetic energy in the turbine, and through friction in materials, not all of that becomes electrical energy.
One alternative is hydroelectric electricity generation. In a hydroelectric system, water is stored in a reservoir, usually a dam, and then allowed to flow downhill to spin a turbine .
This is still energy transfer. Gravitational potential energy when stored becomes kinetic energy when the water is piped to the turbine.
An interesting comparison can be made both to the efficiency in energy conversion of a coal-fired power station, and to the environmental impacts.
Hydroelectric power may appear environmentally friendly; however, it is not without its challenges. The most prominent issue in Australia is the health of the Murray-Darling river system. Prior to the construction of the Snowy Hydro Scheme, snow melts caused flooding along the river system, which effectively washed the river clear of debris, and spread fertile silt over the flood plain. Since the Snowy Hydro Scheme’s dams were built, this has stopped. Further issues have been researched regarding the limited water flow permitted along the river from the dams.
Editors Note: Impacts of these and other issues on ecosystems from the dams all the way to the delta, would be a great study for a stage 3 unit of work combining HSIE and science Key Learning Areas.
Some materials carry the flow of electrons from one atom to the next very well. Elements such as copper and aluminium do this effectively. Silver actually does it the best of all; however, it is expensive. Iron and steel work fairly well too, as does tin and lead. In fact, most metals carry electron flow quite well. Any material that carries electron flow is called a conductor.
All electrical wires and cables are made with conductors, usually from aluminium or copper. Copper is quite flexible, more so than aluminium; however, it does not have as much strength when carrying its own weight. This is why power lines are usually aluminium, which is both lighter and stronger than copper.
Other substances can have conductivity too, such as salt water, or water with impurities like dissolved iron. Carbon can be a conductor as well, although it does not carry current as well as metals. Carbon is used in some electrodes, motor brushes, and other situations for specific reasons.
Other materials don’t allow the electrons to move, without a great deal of voltage to encourage it. These materials are called insulators. Many plastics are insulators, as are wood, concrete, many rocks, and in fact many things that aren’t metal. This is why electrical cables are usually surrounded by a plastic jacket of some sort. The type and thickness of the materials are chosen according to electrical pressure that is applied or expected. This pressure is known as the voltage.
Air is an insulator in its normal form, as are most gasses; however, air under the right conditions can become ionised, at which point it can conduct electricity. This is how lightning travels through air. Any material that is porous can also absorb conductive liquids such as salt water or water with conductors dissolved in it. That is why wooden ladders are now illegal for electricians to use in a workplace; only fibreglass, which is an insulator that doesn’t absorb anything, are now permitted.
All insulating materials can be forced to conduct under sufficiently high pressure, i.e. voltage, with some labs testing at well over 100,000,000 volts. However another class of materials can be made to conduct when required. These materials are called semiconductors. This principle is the foundation for all modern digital electronics, starting from simple transistors, ranging through to integrated circuits, and the most complex computer processors.
The most common material is silicon, with gallium and selenium also used. These chemicals, which are all pure elements, have various other elements added to them in controlled amounts in special processes, known as doping. Doping alters the behaviour of a semiconductor to give certain predictable results. Chemicals such as boron, arsenic, phosphorus, and antimony are used.
Not all electricity comes from a battery or generator. An atom that has lost or gained an electron is called an Ion and is considered to be ionised. Atoms will always attract a replacement for a missing electron, or shed any extra electrons due to an imbalance in the forces between electrons and the nuclei.
In a storm, the thermal energy separates electrons from atoms and the relative motion between clouds and the ground cause polarisation of the clouds. That means that the top of the clouds becomes more positive and the bottom becomes more negative. The clouds now appear like a very big battery .
Nature always tends toward whatever requires the lowest energy, so the clouds may transfer that charge between clouds, or between a cloud and the ground, with spectacular results we call lightning. The terrible damage caused by lightning is evidence that with enough electric pressure, any insulator will conduct.
When electrons flow anywhere, they move in a current, just like water in a pipe. Water flow is measured in litres per minute, and a way of measuring electrical current exists as well. Electrons are very small, the smallest particle of matter that is not still debated. Because they are so small, electrons are measured in huge units called coulombs. One coulomb is 6,240,000,000,000,000,000 electrons. Instead of that large number, it is typically written as 6.24x10^18 electrons, or 6.24E18 electrons, for those who prefer scientific notation! Coulombs are not talked about very much, because instead, a unit called the ampere is used, which is one coulomb of electrons flowing past a point in one second. Ampere is usually pronounced as ‘amp’, and is often written that way too. It is the standard unit to measure and describe electrical current.
When an electron is released from an atom, the electron gains energy. When the electron is captured by another atom, that energy is released as Infra-red light, or what we know as heat. Electrons travelling through a material do so by jumping from atom to atom. Therefore a material that requires more of those hops release more heat energy, and therefore become hotter. Some materials make electron flow very difficult. They are said to have high resistance.
Hopefully this brief overview has established the basics of how electricity occurs and is used. In future editions, topics will progress to how electricity behaves in basic circuits you can build yourself, and how to do some of the basic maths around electronics. You don’t need to remember the fine details of what is presented here; however, being able to follow the process helps in understanding the rules that govern electricity, and why it behaves the way it does.
FOR EDUCATORS: The quantity of energy transferred from coal to electricity would make a great research project for school students. It may suit a particularly engaged stage 3 class, with appropriate scaffolding, and certainly any high school stage. In doing so, cross-curriculum learning is achieved, as science is strongly linked to the sustainability aspect of the geography curriculum. Higher order thinking is promoted by asking students to examine the impacts and alternatives, and propose solutions.Disclaimer: It is illegal in Australia to work on electricity over 50 volts AC or 120 volts DC unless licensed to do so.