Transcript electrical
Electricity is one of the most important forms of energy used in the world today. Without it, there would be no computers, no television, no lights, and no communication. People would have to work and live in a world without many of the conveniences we consider necessary. Transportation in many areas would be hampered or not available, such as the lack of street lights to conduct the flow of traffic. Electricity is everywhere. 2000 years ago the Greeks discovered that when a material that we now call amber was rubbed with some other materials, it became charged with a mysterious force. The charged amber attracted such materials as dried leaves and wood shavings. The Greeks called the amber elektron, which is how the word electricity came about. So, what is an electron exactly? Electron: negatively charged atomic particle that moves around the nucleus of an atom. The Cell in Electrical Currents The cell stores chemical energy and transfers it to electrical energy when a circuit is connected. When two or more cells are connected together, we call this a battery. The cell’s chemical energy is used up pushing a current around a circuit. What happens when the cell’s chemical energy is all used up? The battery dies. What is an electric current? An electric current is a flow of microscopic electrons flowing through wires and components. + - In which direction does the current flow? from the negative terminal to the positive terminal of a cell Simple Circuits When the switch is closed, the lamp lights up. This is because there is a continuous path of metal for the electric current to flow around. If there were any breaks in the circuit, the current could not flow. Circuit Diagram Scientists usually draw electric circuits using symbols; cell lamp switch wires Circuit Diagrams In circuit diagrams components are represented by the following symbols; cell ammeter battery voltmeter switch motor lamp buzzer resistor variable resistor Match the circuit symbols to its correct name in your notes. Electrical Conductors Are objects that allow electrical charge to flow easily EMAPLES: METALS WIRES Electrical Insulators Are objects that do not conduct electricity well EMAPLES: FABRIC PLASTIC WOOD Conductor or Insulator? Cotton balls INSULATOR Cookie Sheet CONDUCTOR Pennies CONDUCTOR Rubber Duck INSULATOR Spatula INSULATOR Chalk INSULATOR Electricity occurs in 2 forms: Static Is stationary Examples: Brush your hair Wool socks in tumble drier Scuff your sock-feet on thick carpet Current Flows around a circuit Examples: Turn on a light Put a phone on a charger Static Electricity Occurs with materials which are insulators Rubbing adds or removes electrons Object becomes charged Like charges repel, unlike charges attract Current Electricity Is the electricity to power appliances, lights, computers, etc. Requires only a flow of electrons around a circuit Since opposite charges attract and like charges repel, the electrons are pushed away from the negative end of the battery or some other power source and drawn back in at the positive end creating a circular flow of electrons. Circuit Types The simplest type of circuit involves electricity going around with no “choices” (electrons don’t really choose). This is called a Series circuit. Draw the path the electrons travel. The other main type of circuit has two or more branches. This is called a Parallel circuit. Draw on the electron flow. Series Circuits Have a single loop for electrons to travel around Components are connected one after another Current has to travel through all components Current is the same at all points Voltage is shared between components Current in a Series Circuit 2A 2A 2A The current in a series circuit is the same at every point so the current must be shared between all bulbs, making them dimmer and dimmer the more you add to the circuit. Parallel Circuits Have two or more paths for electrons to flow down Current is shared between the branches A PARALLEL circuit has more than one path for the current to flow through Assuming all bulbs are the same wattage…they will be the same brightness Current in a Parallel Circuit Advantages of a parallel circuit are: If one bulb fails ….the other will remain on Both bulbs can be switched on separately Resistance Resistance is anything that slows down the flow of electrons Thinner wires offer more resistance causing the wire to heat up and glow (very useful in light bulb filaments) Longer wires also offer more resistance because electrons have further to travel Power rating of appliances: Figuring your monthly energy bill Suppose using 100W for 1 hour costs $0.10 How much would it cost to run the space heater overnight (8 hours)? How much to run the coffee pot/warmer for 2 hours? 1500w • 8hr = 12,000 watts used 300w • 2h = 600 watts used 12,000 / 100 = 120 600 / 100 = 6 120 • .10 = $12.00 for one night 6 • .10 = $0.60 to run for 2 hrs Current Current is the flow of electrons around a circuit There are 2 types: 1. DC = direct current = comes from a battery o DC – direct current (battery) Electrons flow in one direction AC = alternating current = comes from electric companies 2. o Electron flow changes direction 50 times per second AC – alternating current (generator) Direct Current (DC) Direct Current (DC) always flows in the same direction, but it may increase and decrease. Electronic circuits (like computers) normally require a steady DC supply which is constant at one value or a smooth DC supply which has a very small variation called ripple. Cells, batteries and regulated power supplies provide steady DC which is ideal for electronic circuits. Lamps, heaters and some types of motors will also work with any DC supply. Alternating Current (AC) Alternating Current (AC) flows one way, then the other way, continually reversing direction. An AC voltage is continually changing between positive (+) and negative (-). The rate of direction change is called the frequency of the AC and it is measured in hertz (Hz) which is the number of forwards-backwards cycles per second. It is used in power grid transmission and distribution systems because AC can be easily and efficiently converted from one voltage to another using a transformer. Power Grids: Getting energy from the power plants to your home. Trace the path from the power plant to a lamp in your home and put the parts in order. 2 8 7 9 6 4 3 1 5 Transmission Substation Outlet Junction Box (on the side of house) Electric Circuit of a Lamp Transformer Drum Power Substation High Voltage Transmission Lines Power Plant Power Poles Generating Electricity Recall that electricity is just the flow of electrons. To make them flow (generate electricity), all you have to do is spin a coil of wire inside a magnet. Of course the larger the coil and magnets, the more electricity you can create. Power Generator A generator transforms mechanical energy into electrical energy Turbines Turbines can spin super large coils through super large magnets to generate massive amounts of electricity. Power plants usually use steam to turn the turbines. So what do they burn to boil water and make steam? Fossil fuels Producing Electricity at a Power Plant 1. Fuel (fossil fuels) produces heat, which is used to boil water to make steam. 2. Steam spins a turbine. 3. The turbine drives a generator and the generator makes electricity. 4. Electricity goes to the transformers to produce the correct voltage.