SYSTEMS : ELECTRICITY

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. 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 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.

WHERE DOES ELECTICITY WE USE COME FROM? 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.

CELLS The cell is another common source of electricity. (e.g. batteries) 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.

WEBSITES TO VISIT FOR MORE INFORMATION Much of the information in these slides have been extracted from the following websites: http://www.energyquest.ca.gov http://www.science.howstuffworks.com/battery.htm http://www.science.howstuffworks.com/solar-cell.htm http://www.eia.doe.gov/kids/electricity.html Please go to the above websites for more detailed information about electricity.