B - A - 3.4 - Generation of Electricity.pdf

Module 3: Electrical Fundaments Topic 3.4: Generation of Electricity  INTRODUCTION On completion of this topic you should be able to: 3.4.1 Define the production of electricity by the following methods: Light...

Module 3: Electrical Fundaments Topic 3.4: Generation of Electricity  INTRODUCTION On completion of this topic you should be able to: 3.4.1 Define the production of electricity by the following methods: Light Heat Friction Pressure Chemical Action Magnetism and motion 30-03-2024 Slide No. 2  ATOMIC STRUCTURE OF MATTER Atom - comprised of a nucleus in the centre with electrons spinning around the outside in shells. Hydrogen atom is the simplest. Nucleus - always positively charged. Hydrogen atom - only one proton (positively charged) in its nucleus. Number of electrons spinning around the nucleus, always equals number of protons within the nucleus. Hydrogen atom has only one electron. Hydrogen Atom 30-03-2024 Slide No. 3  ATOMIC STRUCTURE OF MATTER Electrons in outer orbits attracted to the nucleus by less force than electrons near the nucleus. Outer electrons easily forced from their orbits. In some materials they leave their orbits and wander among the atoms at random – Free Electrons. Outermost Electrons – Valence Electrons. Motion of the free electrons – electric current. 30-03-2024 Slide No. 4  ELECTRON THEORY When a positive charge is applied to an atom the outer electron is drawn away. Leaves the atom with more protons than electrons - exhibits a positive charge (now called a positive Ion). Positively charged ion attracts electrons from surrounding atoms and draws away the valence electrons. Flow of electrons toward a positively charged source is called. “ELECTRON FLOW” Nucleus of a copper atom 30-03-2024 Slide No. 5  ELECTRON THEORY A conductor made of copper is connected across a source of electrons. The positive terminal of the source attracts an electron. This atom is now a positively charged ion. The +ve ion now pulls an electron from the next atom along. Exchange continues until electron is replaced by one from the sources negative terminal. Flow of electrons toward a positively charged source is called. “ELECTRON FLOW” 30-03-2024 Slide No. 6  ELECTRON THEORY Electron movement takes place within the conductor at the speed of light. Electron enters conductor – immediately forces one from other end. You cannot see electrons, but you can see and feel the effects: Magnetic field Heat 30-03-2024 Slide No. 7  ELECTRON THEORY Electrons flow from -ve to +ve. The flow of electrons perform work: Lighting Heating Electric motors Electronic applications An imbalance in electrical potential creates an electron driving force – Electro-Motive Force or EMF. Electricity is generated by producing an EMF, or an imbalance in potential. 30-03-2024 Slide No. 8  POTENTIAL DIFFERENCE Potential difference of one electron is of no practical use. A difference of 6,250,000,000,000,000,000 electrons (six quintillion, two hundred and fifty quadrillion) equals 1 volt. When switch is turned on electrons flow from one potential difference to the other. Rate of electron flow is proportional to the potential difference. 30-03-2024 Slide No. 9  TYPES OF ELECTRICITY Two basic types of electricity: Current Static In current electricity, electrons move through a circuit and perform work. Static electricity is more of a nuisance. 30-03-2024 Slide No. 10  VOLTAGE PRODUCED BY FRICTION Two materials are rubbed together, electrons are “wiped off” one onto the other. Looses electrons – electrically +ve; gains electrons electrically –ve. Good conductors equalise charges as fast as they are created. Poor conductors – little equalising current – electrostatic charge builds up readily. Static charge more readily created between non-conducting materials. 30-03-2024 Slide No. 11  VOLTAGE PRODUCED BY FRICTION Static electricity – Real concern during fuelling operations. Movement of fuel through a rubber transfer hose has same effect as rubbing a rod. with a piece of fur (relative movement) – builds up huge potential differences. Aircraft movement through the air can build up huge potential charges on the aircraft skin which can cause sparking when back on the ground. Aircraft earthing and electrical bonding are critically important. 30-03-2024 Slide No. 12  VOLTAGE PRODUCED BY PRESSURE Compress a quartz crystal – charges appear on opposite surfaces. Can be used to convert mechanical energy into electrical energy. Piezoelectric effect. Not suitable for large voltage or power requirements. Microphones and barbecue lighters use this principle. 30-03-2024 Slide No. 13  VOLTAGE PRODUCED BY HEAT When copper is heated, valence electrons move toward cooler end. In iron, the opposite takes place – electrons move toward hot end. Electrons flow through the hot junction. Electron flow is proportional to intensity of heat. Electron flow (current) is measured to provide temperature indication. Thermocouples use this principle. 30-03-2024 Slide No. 14  VOLTAGE PRODUCED BY LIGHT Light has energy – like any moving force. Some metallic substances sensitive to light. Light strikes the surface and dislodges valence electrons. Upon losing electrons – photosensitive metal becomes positively charged. EMF produced is called photoelectric voltage. 30-03-2024 Slide No. 15  VOLTAGE PRODUCED BY LIGHT Photo-cell Cell has a curved, light-sensitive surface focused on a central anode. Light strikes the sensitive surface and electrons are emitted toward the anode. Power capacity is very small. Photocell is useful in detecting or accurately controlling many operations. 30-03-2024 Slide No. 16  VOLTAGE PRODUCED BY CHEMICAL ACTION Two dissimilar metallic materials immersed in a solution to produce a chemical action. One material has greater chemical action than the other, charged ions are formed and an EMF is produced. Wet cells have liquid electrolyte and must remain upright. Common use - motor vehicle batteries. Dry cells have electrolyte mixed to form a paste. Common use - torch and radio batteries. 30-03-2024 Slide No. 17  VOLTAGE PRODUCED BY MAGNETISM AND MOTION Three fundamental conditions must exist before a voltage can be produced by magnetism: Must be a conductor in which voltage will be produced Must be a magnetic field in conductor's vicinity Must be relative motion between field and conductor Conductor must be moved to cut magnetic lines of force, or magnetic field must be moved so flux cuts across conductor. When conductor cuts the lines of force, electrons are propelled in one direction. This creates the electric force or voltage. 30-03-2024 Slide No. 18  VOLTAGE PRODUCED BY MAGNETISM Electromagnetic induction is the most common form of power generation. Aircraft generators and alternators. Atomic, hydro-electric and fossil fuel power plants. Amount of electricity produced depends on the rate at which lines of flux are cut. Rate can be increased by: Increasing magnet strength Increasing conductor speed Increasing number of conductors 30-03-2024 Slide No. 19  VOLTAGE PRODUCED BY MAGNETISM SUMMARY Spinning a loop of wire in a magnetic field generates an EMF. It doesn’t matter what drives the loop – must be relative motion between conductor and lines of magnetic flux. Voltage produced because valence electrons forced from atoms by magnetic field. An imbalance in electrons causes electron flow this is electricity. 6,250,000,000,000,000,000 electrons per volt. 30-03-2024 Slide No. 20  CONCLUSION Now that you have completed this topic, you should be able to: 3.4.1 Define the production of electricity by the following methods : Light Heat Friction Pressure Chemical Action Magnetism and motion 30-03-2024 Slide No. 21  This concludes: Module 3: Electrical Fundaments Topic 3.4: Generation of Electricity