SYSTEMS : ELECTRICITY Lesson 1: How important is electricity to us? Where does it come from? Is it important to conserve it?

Where do we get our electricity from? There are several sources of electricity but we will focus on the power generator today. An electric generator is a device for converting mechanical energy into electrical energy. The process is based on the relationship between magnetism and electricity. When a wire or any other electrically conductive material moves across a magnetic field, electricity flows in the wire.

POWER GENERATORS This generator is based on the principle of “electromagnetic induction” discovered in 1831 by Michael Faraday, a British scientist. To make electricity therefore, we need to somehow keep turning the coil of wire. The normal way is to use a turbine which is a fan in reverse (Wheel and axle)

POWER GENERATORS But what turns the turbine then? Wind generators are probably the easiest type of power station to understand. Advantages : Clean and damage the environment very little Disadvantages: Unsightly Produce a lot of noise Rarely built in inhabited areas – power must be transmitted long distances and power is lost. Wind is not controllable and not always available.

POWER GENERATORS The next easiest to understand type of power station is the hydroelectric station. Here the turbine is driven by moving water rather than moving air. Advantage: Turned on very quickly, within seconds, sudden increase in supply of electricity Renewable resource Disadvantage: Depends on where the river is and again long transmission distance

POWER GENERATORS The third and by far the most important way of driving the turbines is steam. In a power plant, there are big boilers that burn a fuel to make heat so that steam is produced when the water has boiled. The steam is then piped to the turbine through very thick pipes. The steam is fed under high pressure to the turbine which spins and its shaft is connected to the turbogenerator. First disadvantage is that a lot of CO2 is produced.

POWER GENERATORS

How electricity is produced in a power station 2. Steam is produced. 3. Steam turns the turbine. 4. The turbine is connected to a generator. As the turbine turns, the generator spins and produces electricity. boiler steam turbine generator 1. Oil, coal and natural gas are burnt to boil water. © 2009 Marshall Cavendish International (Singapore) Private Limited

POWER GENERATORS The question next is what is burnt to produce the heat. The fuel used is usually wood, coal, oil or natural gas. These fuels are the remains of plants and animals that lived million of years ago. It takes many years to form and cannot last forever. Such fuel is non- renewable. Once they are gone, they’re gone. So, new ways of heating water using renewable resources are constantly being thought of and used.

POWER GENERATORS Nuclear power plants use nuclear energy to heat water. (small amounts of extremely hazardous waste) Geothermal power plants use steam or hot water found naturally below the earth’s surface without burning a fuel. Hydroelectric power stations uses flowing water to spin the turbine. Solar power, wind power, tidal energy or biomass are also used. Each has its advantages and disadvantages.

SYSTEMS : ELECTRICITY Lesson 2 : What is electricity in the first place?

What is electricity? To understand what is electricity, we need to know a little bit about atoms and their structure. All matter is made up of atoms, and atoms are made up of smaller particles, mainly the proton, neutron and the electron. Electrons spin around the centre, or nucleus of atoms while the nucleus is made up of neutrons and protons.

What is electricity? Electrons contain a negative charge, protons a positive and neutrons are neutral. There are many kinds of atoms, one for each type of the 118 different known elements. Each atom has a specific number of electrons, protons and neutrons.

What is electricity? Usually, number of electrons = number of protons. When this is the case, the atom is balanced and stable. However, some kinds of atoms have loosely attached electrons. They are easily disturbed by outside forces and may lose some electrons and become positively charged or gain some electrons and become negatively charged. A charged atom is called an ion. It is this movement of electrons from one atom to another that creates a current of electricity.

What is electricity? Electricity is conducted through some things better than others do. Some materials are very resistant. Their atoms hold their electrons very tightly so they cannot move very well. These things are called insulators. (Can you give some examples?) E.g. rubber, plastic, cloth, glass, dry air etc. Some materials have loosely held electrons which move through them very easily. These are called Conductors e.g. most metals like copper, aluminium, steel etc.

What is electricity? When people first studied the flow of electric current in metal wires, they thought that a current was a flow of positive charges moving out from the positive end of an electrical source to the negative end. Later they discovered that the current is actually a flow of electrons moving from the negative end to the positive end. The electrical source provides the push and the electrons start moving. However, they kept the convention and we still draw current as flowing from the positive terminal of a cell to the negative terminal. (conventional current)

WHERE DOES ELECTICITY WE USE COME FROM? We get electricity from the conversion of other sources of energy, like coal, natural gas, oil, nuclear power and other natural sources, which we call primary sources. In the past before electricity was discovered, people used primary sources to provide us with light, heat, cooked food etc. After Benjamin Franklin’s experiment with a kite one stormy night in Philadelphia and principles of electricity gradually becoming understood, we relied on electricity more and more to provide us energy.

A natural source of electricity is the lightning. For households, we get our electricity from the power generator. We can also get electricity from dry cells and even solar cells. WHERE DOES ELECTICITY WE USE COME FROM?

CELLS The cell is another common source of electricity. A cell stores chemical energy and changes it to electrical energy when needed. The current produced by a cell is direct current (DC) which flows in one direction.

CELLS Inside the battery, a reaction between chemicals take place. The reaction causes electrons to be released. It then flows through the wires connected, creating a circuit. There are two types of cells: namely, primary cell and secondary cell.

CELLS Primary cells have limited lifespans. The chemical reactions inside the cells that produce electricity are non-reversible. Hence the cells cannot be reused once the chemicals are used up. Dry cells are examples of primary cells. When two or more dry cells are connected together correctly, they are called a battery. Secondary cells can be recharged e.g. lead-acid accumulator used in the laboratories and cars.

SOLAR CELLS They convert sunlight directly into electricity. If only we could collect all of the sun’s energy, we could power our homes and offices for free. However, can this be done? The solar cells are photovoltaic cells made of special materials called semiconductors such as silicon.

SOLAR CELLS Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material. This energy knocks electrons loose, allowing them to flow freely. So by placing metal contacts on the top and bottom of the cell, we can draw that current off to use externally.

Saving energy Energy for the generators can also come from other sources. Generators in windmills make use of wind to move, while generators in dams use running water. windmills dam © 2009 Marshall Cavendish International (Singapore) Private Limited

Saving energy Oil, coal and natural gas are natural resource that come from the Earth. The more we use them, the less we will have for the future. This is because oil, coal and natural gas take a long time to be formed and cannot be replaced quickly when they are used up. An oil rig drills for oil from the seabed. coal © 2009 Marshall Cavendish International (Singapore) Private Limited

Saving energy We have to use these resources carefully so that they do not get used up too quickly. When we waste electricity, we are indirectly wasting these resources too. Thus, it is important for us to conserve electricity. © 2009 Marshall Cavendish International (Singapore) Private Limited

Saving energy There are many ways to conserve electrical energy. –Switch off all electrical equipment that are not in use. –Use energy-saving bulbs. These bulbs use less electricity, but produce sufficient light. –Do not open the door of the refrigerator unnecessarily. Each time the door is opened, more electricity is needed to cool the refrigerator. © 2009 Marshall Cavendish International (Singapore) Private Limited

Saving energy There are many ways to conserve electrical energy. –Use electrical equipment that switch off automatically. –At night, sleep with the lights off. If you really need to have some light, use a small lamp. timer © 2009 Marshall Cavendish International (Singapore) Private Limited

Saving energy Conserving electrical energy in these ways can allow oil, coal and natural gas to last longer. It can also help your family save money. © 2009 Marshall Cavendish International (Singapore) Private Limited

WEBSITES TO VISIT FOR MORE INFORMATION Much of the information in these slides have been extracted from the following websites: (how power stations work) Please go to the above websites for more detailed information about electricity.