How Power Works

In ‘How Power Works’ our aim is to provide as much valuable and educational information/ resource regarding power. The Information is theory driven and has been sourced from various sources that have been acknowledged.

Natural Power Solutions hopes to provide information which will assist in you selecting the correct Power solution.

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History of electricity

The Greeks first discovered electricity about 3000 years ago. Its name came from the word 'elektron', which means amber. Amber is a yellow, fossilised rock found in tree sap, and the Greeks found that if they rubbed amber against wool, lightweight objects (such as straw or feathers) would stick to it. This form of electricity is known as static electricity.

The American writer, scientist, diplomat and inventor, Benjamin Franklin, started working with electricity in the 1740s. He performed different experiments to try to understand more about it, and eventually proved that lightning (a form of static electricity) flowed like water.

In 1821, English scientist Michael Faraday discovered how to make an electrical current. He found that when a magnet spins inside a coil of copper wire, a tiny electrical current flows through the wire, creating an electrical charge. This is the principle of how electricity is made today.

In 1879, American inventor Thomas Edison developed the first practical incandescent lamp. Edison also developed a new direct current generator which, when coupled with a steam engine, made today's large-scale electricity generation possible.

A history of gadgets and gizmos

From 1935 electrical devices were discovered at an increasing rate. Some of the highlights include:

  • 1935 The orange sodium vapour lamp commonly used in street lighting was invented. Hearing aids which ran from batteries, rather than aids with large horns attached, were used for the first time.
  • 1936 The upright Hoover vacuum cleaner was released. The first fluorescent tube was produced. The first thermostatically controlled iron went on sale.
  • 1937 The first photocopier was demonstrated.
  • 1938 Thermostats were first used in ovens.
  • 1939 The first studies on solar houses were made. Hand-held electric slicing knives introduced.
  • 1940 The isotope of Uranium, U-235, used in nuclear reactors was isolated for the first time. The first gas powered station for generating electricity was opened in Switzerland.
  • 1941 The first windmill connected to an electrical grid system came into operation.
  • 1942 The first controlled, self-sustaining nuclear reaction occurred.
  • 1943 The first operational nuclear reactor was built.
  • 1944 The first automatic, digital computer went into operation. The first searches for oil took place.
  • 1945 Enormous oil reserves discovered in Saudi Arabia.
  • 1946 First car telephones used. The rotary clothes hoist invented in Australia.
  • 1947 Use of Xenon in lighthouses. First microwave ovens produced.
  • 1948 The Polaroid camera was developed.
  • 1949 RCA developed the first 45 rpm record.
  • 1950 The first radio-paging service was started. The first nuclear accident occurred in Canada.

After 1950 there were many more developments and discoveries in electrical devices. If you want to know more use your library and the Internet. You can visit the energy museum at www.energymuseum.com.au

Electrical terms and units of measure

Power

Power is the rate at which energy is produced or used. The unit of measurement for power is the watt (W).

If you examine a light bulb carefully you will see that it has maybe "45, 60 or 100 watts" written on it. If it has "60 watts" written on it this means that it uses 60 joules of energy for every second it is on.

If a power station has an output of 600 megawatts (MW) of electrical power, it is producing 600 000 000 joules of energy every second. Imagine how many light bulbs that would keep going!

Voltage

The volt is named in honour of Alessandro Volta, an Italian scientist.

Voltage is the difference of electrical potential between two points of an electrical or electronic circuit, expressed in volts. It measures the potential energy of an electric field to cause an electric current in an electrical conductor. Depending on the difference of electrical potential it is called extra low voltage, low voltage, high voltage or extra high voltage.

Voltage is the unit of measure for electro-motive force required to pass one ampere through a resistance of one ohm (see "Resistance" below).

A simple way to understand voltage is to compare electricity flowing through a wire to water flowing through a pipe. If you pump water through a 100 metre long pipe with a small diameter, the water will barely flow out the other end. This is because there is a certain amount of friction which increases relative to the length of the pipe. Two things can increase the flow of water:

  1. Making the pipe diameter larger (thus decreasing resistance);
  2. Increase the pressure of the water (or voltage).

If electricity is to be transported over long distances, the resistance in the conductor (known as ohms) must be accounted for. Therefore, the diameter of the conductors and the voltage ("pressure") must be increased.

Electricity is generated at a comparatively low voltage at a generating (power) station. One of the voltages used by Queensland power generators is 15 750 volts. In order to transport this electricity over long distances, the voltage must be increased to as high as 275 000 volts by transformers.

Ampere

The ampere (or "amp"), named after the French scientist Andre Maria Ampere, is a measure applied to the flow of electrons. An "amp" is a unit of measurement for electrical current.

One ampere represents the rate of 1 coulomb of charge per second. A coulomb is equivalent to 6.24 X 1018 electron charges, hence a current of one amp means a flow of 6.24 X 1018 electron charges passes any given cross section of the conductor per second.

Resistance ohm

The German scientist Georg Simon Ohm discovered that in any conductor, electrons encounter a resistance whilst flowing through a circuit. He proved experimentally that the current in a metallic conductor is directly proportional to the voltage between its ends.

Therefore,

The unit of resistance is the volt per ampere. A resistance of one volt per ampere is called one ohm. That is, the resistance of a conductor is one ohm if the voltage between the ends of the conductor is one volt when the current in the conductor is one ampere.

Power

A watt is the unit of electric power. One watt is a measure of the power consumed when a current of one "ampere" flows under a pressure of one "volt".

Electrical arithmetic

On all electrical appliances you will find the "rating" marked in watts (for example, iron - 600 watts, heater - 1 000 watts, lamps - 100 watts. The power taken by any appliance (such as a toaster, heater, kettle etc.) is found by multiplying the voltage by the current:

watts = volts X amperes (Amps)

and

1000 watts = 1 Kilowatt (kW)

1,000,000 watts = 1 Megawatt (MW)

A watt-hour is the amount of energy consumed by an appliance in one hour if it operates at a power of one watt. A watt-hour is too small a unit for most purposes, so we use the "kilowatt-hour" (kWh), which is equal to 1000 watt-hours. Kilowatt-hours are the units measured by the electricity meter in your home.

1 kilowatt hour (kWh) = 1000 watt hours

To find the number of kilowatt-hours used by an appliance in any period, multiply the rating in watts by the number of hours in operation and divide by 1000:

The number of hours required for an appliance to use one kilowatt-hour is found by dividing 1000 by the rating in watts.

Thus, a 1000 watt radiator would take one hour to consume 1 kWh, but a 100 watt lamp would take 10 hours.

An average home (three bedroom home occupied by two adults and two children) uses an average of 17kWh per day.

When working out how much electricity is used by each appliance in your home, remember that some things like electric irons are only using power intermittently, as they are switched on and off either automatically or by hand.

We have all been exposed to electricity in one form or another. We see it produce lightning in a summer thunder storm or we get an electrical shock as we step out of the car on a cold dry day. We see electricity light our cities, heat or cool our homes, cook our meals and run our computers.

As long ago as 600 BC, the Greeks discovered that by rubbing amber with wool it was able to attract lighter objects. In today's terms we would say that the amber was electrified or had become electrically charged.

There is no easy definition for the term electricity, which requires an understanding of the structure of matter, forces, work and energy.

To be better able to answer the question "What is electricity?" we need to examine some fundamental and sometimes complex concepts.

  • Electrostatics
  • How do objects become electrically charged?
  • Conservation of charge
  • What is electrical charge measured in?
  • Coulomb's Law - the force between charged objects
  • How do objects become electrically charged?
  • Charging by conduction
  • Charging by induction
  • Electric Fields
  • Electric Potential Energy
  • So what is voltage?

Electrostatics

Electrification is the process by which an object becomes electrically charged. The two forms of electrical charge are positive and negative.

When two electrically charged objects are placed near each other they exert a force on each other.

If the objects have the same charge then they will repel and if they carry different charges, they will attract.

How do objects become electrically charged?

In order to answer this question, we will first examine the atomic nature of matter.

All matter is made up of atoms. An atom is a particle that has a positively charged nucleus that is made up of protons and neutrons1 and is surrounded by a negatively charged electron cloud. Protons (p+) have a positive charge, electrons (e-) a negative charge and neutrons (no) no charge.

An atom is electrically neutral when the number of protons equals the number of electrons. For example, a neutral lithium atom has three protons in its nucleus and three electrons in the electron cloud. This gives the atom a net charge of zero.

1 The exception to this is the hydrogen atom where its nucleus is made up of a single proton. Isotopes of hydrogen can have 1 or 2 neutrons.

An object is electrically neutral when it has an equal number of positive charges and electric charges. The object becomes electrically charged when it either loses or gains electrons. This can occur when a plastic rod is rubbed with a nylon cloth.

An object is electrically charged when there is a difference between the number of positive and negative charges. If there is a difference, then we say that there is a net charge on the object.

For example, if an object had 10 positive charges and 8 negative charges then we would say that the object carries a net positive charge.

An object can never lose or gain positive charges: only electrons can be transferred between objects.

Conservation of charge

The conservation of charge law states that the amount of charge in a closed system always remains the same (a closed system is one that cannot be externally influenced). On a grander scale, the conservation law means that the amount of charge in the universe always remains the same.

What is electrical charge measured in?

The net charge of objects can vary. This means that an electrically charged object has a quantity of net charge that can be measured. The unit that we measure electrical charge in is the Coulomb (C). The symbol for charge is q (just as we use m as the symbol for mass with the unit of measurement being the kilogram (kg).

The charge on a single electron is -1.6 x 10-19 C and the charge on a single proton is +1.6 x 10-19 C.

Note: the charge on the proton and electron have the same value but are opposite in sign. The charge on a neutron is zero.

Coulomb's Law - the force between charged objects

When two objects carrying a net charge are placed near each other they experience a force of attraction or repulsion. In 1785 Charles Augustine Coulomb conducted experiments that examined the force that existed between charged objects.

From his experiments he determined that the force between two charged objects was proportional to the product of the charges and inversely proportional to the square of the distance between their centres. This is called Coulomb's Law.

Coulomb's Law - the formula for the force between two electrically charged objects

where:

F = force measured in Newtons (N);
r = the distance between the centres of the two objects measured in metres (m);
q = the charge on the two objects measured in Coulombs (C);
k = constant of proportionality which has a value of 8.9874 x 109 Nm2C-2.

Remember this force can cause the objects to repel or attract depending on the charge of the objects.

Note: this formula refers to the force exerted by point charges and varies with distance.

The term "point charge" refers to a charge that has no mass so that the influence of gravitational forces can be neglected.

How do objects become electrically charged?

If you drive in a car on a cold dry day you might experience an electrical shock as you step out of the vehicle. This occurs because the car builds up an electrical charge and "earths" or flows through you when you step on the ground.

In other words you act as an electrical conductor, in the process giving you an electrical shock.

So how do objects become electrically charged? Objects become electrically charge through a process of conduction or induction.

Charging by conduction

An electrically neutral object is charged by conduction when a charged object comes into contact with it.

For example when a rod (that has an excess of electrons) touches a neutral ball the charge distributes itself over both objects.

When they are separated, the ball will now be electrically charged.

Charging by induction

Charging an electrically neutral object by induction is a three-step process.

  1. Let's suppose a negatively charged rod is brought close to an electrically neutral ball. The electrons on the ball are repelled and move to the opposite side of the ball.
  2. By touching the negative side of the ball, the electrons are then "earthed" off. In other words the electrons flow from the ball leaving it with a net positive charge.
  3. The rod is then removed leaving a positively charged ball.

Electric fields

Any object carrying electrical charge, whether it is static or current, will generate an electric field.

So what is an electric field? Put simply, if an electrically charged object is placed in an electrical field it will experience a force.

Electrical fields come in two varieties: uniform and non-uniform. If a charged object is placed in a uniform field then it will experience the same force no matter where it is placed in the field.

If it is placed in a non-uniform field then the force may vary depending on the position of the charge.

Lines represent electric fields diagrammatically, with arrows indicating the direction of the field.

An important point to remember about an electric field is that it is a vector quantity so it has magnitude and direction.

Electric field strength

In discussing this topic we will talk about point charges, which have no mass but carry an electrical charge.

By convention (in other words everyone has agreed) that the direction of electric fields is determined with respect to a positive charge.

Note that the field lines move away from the positive charge and toward a negative charge. This means is that if a positive test charge is placed in these fields then it will move away from the positive charge and toward the negative charge.

The arrows on the field lines indicate the direction a positive charge will move if it is placed in the electric field. If a negative charge is placed in an electric field it will move in the opposite direction of the field lines.

The strength of the electric field is defined as the force per Coulomb. For example if a 10 C charge were placed in an electric field of strength 10 NC-1, then it would experience a force of 100 N. The strength of an electric field can be calculated by the following:

Formula to calculate electric field strength

where:

F = force measured in Newtons (N);
qt = charge in Coulombs (C);
E = electric field strength in Newtons per Coulomb (NC-1).

Non-uniform field - electric field strength of a point charge

Recall that there are two types of electric fields: uniform and non-uniform. A point charge will produce a non-uniform field. This means that the electric field strength will change depending on the distance from the charge.

Formula for Electric Field Strength

Now remember that and then:

where:

F = electric field strength of a point charge (q);
r = the distance between the centres of the two objects measured in metres (m);
q = the charge on the two objects measured in Coulombs (C);
k = constant of proportionality which has a value of 8.9874 x 109 Nm2C-2.

Uniform electric fields - the field between two parallel plates

When two metal plates are connected to the terminals of a battery then they each gain a net positive and negative charge.

This results in a uniform electric field being generated between the two plates.

It is uniform because its strength does not vary with position. That is if a positive charge were placed within the field it would experience the same force irrespective of its position.

The electric field strength is still determined by:

where:

E = electric field strength,
F = force and
qt = charge

This concept is important in understanding how an electrical current is generated.

Electric Potential Energy

If you have studied mechanics then you would have come across the concept of gravitational potential energy.

You may remember that a body gains gravitational potential energy as it is lifted above the ground - work is done against the force due to gravity.

If the object is allowed to fall then it will gain kinetic energy or energy of movement.

Charged objects can experience the same phenomenon. That is, the electric potential energy of a charged object can be converted to kinetic energy.

If you want to move the charge at point A to point B then you would have to work against the electric field.

When the charge reaches point B, then we say that it has gained electrical potential energy.

If the charge is allowed to move from B to A then it will gain kinetic energy. When this happens an electric current is produced.

So what is voltage?

If you look at the previous diagram then at point A the charge has a certain electrical potential. At point B the charge would have a different potential. The difference between these two points is called the potential difference - this is commonly called the voltage.

The potential difference (or voltage) is the work required to move a unit of positive test charge from A to B and can be measured in volts (V).

Another way of describing potential difference is that it is the energy per unit charge required to move from A to B.

To calculate potential difference between points A and B we need to know the work done on the charge.

i.e. Work done on a charge q = force x distance

where:

E = Electric field strength
q = charge
d = distance charge is being moved

So what does it all mean?

The human race is no different from the animals and plants on this planet - it needs energy to survive. The human body gets its energy from the food it consumes which ultimately comes from the sun.

What makes us different is that we have learnt how to harness energy and use it as a tool that powers our society.

One of the biggest advances in our technology was to find a way of easily transporting energy from one point to another and being able to easily transform energy from one form to another. We call this electricity. The keyword is move - we must get those electrons moving in order to produce electricity.

Recall that if a charged particle, such as an electron, is placed in an electric field it experiences a force. This force causes it to move. Any moving charge creates an electric current.

Metal conductors (as found in a piece of electrical wire) have what is called "free electrons". If the wire is connected to the terminals of a battery then a uniform electric field is created in the wire. The free electrons then move from the negative terminal to the positive terminal creating an electric current.

If you imagine a city connected to the terminals of a power station, an electric field is created in all the electrical conductors, which in turn causes the free electrons to move, creating an electric current. If we are to harness electricity as a tool we need to have an understanding of the fundamentals in order to use it effectively.

How Power Works information used with permission from energex ltd - www.energex.com.au

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