Current Electricity (PDF)

## CURRENT ELECTRICITY In chapter 11 you learned that static electricity can build up on the surface of objects until it is discharged. **Current electricity** refers to electric charges (electrons) that flow through a conductor in a controlled way (for example, through wires made of metals like...

## CURRENT ELECTRICITY In chapter 11 you learned that static electricity can build up on the surface of objects until it is discharged. **Current electricity** refers to electric charges (electrons) that flow through a conductor in a controlled way (for example, through wires made of metals like copper or aluminum). Current electricity can be provided using batteries or from an electrical generating station (the source is from the wall outlets you see). Electronic devices all require a flow of electrons to operate. This continuous path for electron flow is an **electric circuit**. There are two forms of current electricity: 1. **DIRECT CURRENT (DC):** - A flow of electrons in one direction through an electric circuit. - Produced by an electric cell to power small devices. 2. **ALTERNATING CURRENT (AC):** - Flow of electrons that alternates in direction through an electric circuit. - Produced by generating stations (wall outlets) to power lights and large devices. - AC is used in electric generating stations because it is a more efficient method of distributing electrical energy over long distances than DC. ## ELECTRIC CIRCUITS Electrons flowing through an electric circuit using wires as a controlled path can be compared to your circulatory system. Blood flows around but always comes back to your heart and repeats the circuit. Electric circuits include FOUR things: 1. **Energy source:** - This can be as small and portable as a battery, or as large as a generating station. 2. **A load:** - This is a device that transforms electrical energy into other usable forms of energy. Examples are heaters, lamps, fans, computer hard drives, and microchips. 3. **Conducting wires:** - They join all the parts of an electric circuit together. They provide a path for the electrons. 4. **(Sometimes) - a switch:** - Controls the flow in an electric circuit. Often used to control household devices. - **OPEN CIRCUIT** - switch is off. Broken connection in the loop. No electricity can flow. - **CLOSED CIRCUIT** - switch is on. Wires are all connected in the loop. Electricity flows. ## ELECTRICAL ENERGY Electrical energy is the energy that is provided by the flow of electrons in an electric circuit. **SOURCES OF ELECTRICAL ENERGY** Electrical energy may not always come from a generating station. It can also come from: 1. **Electric Cells** - A portable device that converts chemical energy into electrical energy. - It has two electrodes. The top (or bump) of the battery is the positive terminal and the bottom is the negative. - We use the word "battery" to refer to an electric cell but the term "battery" really means two or more electric cells in combination. - **Primary cells** are cells that cannot be recharged. - **Secondary cells** can be recharged and reused many times before they are recycled. - Batteries are toxic to the environment and should always be properly recycled. 2. **Fuel Cells:** - This is a special kind of electric cell through which a continuous supply of chemicals is pumped as the cell operates. - This means that a fuel cell can operate for far longer than a conventional electric cell. - For example, the hydrogen fuel cell produces electricity by converting hydrogen and oxygen into water. The fuel (hydrogen and oxygen) react to produce electricity. - There are fuel cell vehicles (FCV's) that are becoming more popular because there are no toxic gases when operating... just water comes out of the tailpipe! ## GENERATING ELECTRICITY Electricity is produced when one type of energy is converted into electrical energy. Generating stations convert mechanical energy into electrical energy. Some external force must push the blades of a turbine, causing it to turn. Inside the turbine, a coil of wire in the generator rotates near a magnet, causing electrons to flow. Electrical energy is special because unlike other forms of energy, its production can be controlled and it can travel long distances to where it will eventually be used. ### GENERATING USING RENEWABLE SOURCES **WATER GENERATION** - This is hydro-electric generation. The energy of falling water is used to turn the turbine. - The generating stations use the fast-moving water of a waterfall or river, or the water stored in a reservoir behind a dam. - Water power is a renewable resource because the natural resource here is continually replenished and will never run out (except severe droughts). - **Pros:** doesn't pollute air or water. - **Cons:** not always suitable locations, vast amounts of resources needed, damages the ecosystem by flooding. **TIDAL GENERATION** - Movement of the ocean tides back and forth can be used to generate electricity. - Tides are cyclical and the movement of the tides can be used over and over again. - **Pros:** no pollution - **Cons:** can only be built near coastlines with large tides. **WIND GENERATION** - A wind turbine consists of large blades mounted on a tall tower. - As the wind blows, it turns a turbine which is connected to a generator. Each single wind turbine can generate enough electricity to power 250 Canadian homes. - **Pros:** Can be located near where the power is needed so there are less transmission lines. Doesn't pollute air or water. - **Cons:** Wind isn't always blowing! **SOLAR GENERATION** - Solar panels, or photovoltaic cells converts light directly into electrical energy. This is renewable as the Sun is always there. - **Pros:** Doesn't pollute air or water. Can operate independently of an electrical grid. Maintenance-free. - **Cons:** Less than 30% efficient, and very expensive. The Sun is out only for a limited time. ## ENERGUIDE and ENERGY STAR LABELS All household appliances are sold with an Energuide label to help consumers make informed choices. It provides an estimate of how much electrical energy (measured in kilowatt-hours) the appliance will use in one year. There is also a "phantom" load which is small amounts of energy that are always used by appliances even when they're off. This can be small lights, or a sensor waiting to sense the "on" switch when it is selected. ## GEOTHERMAL ENERGY - Liquid is circulated through deep pipes in the ground where the heat from the Earth's crust is transferred to this liquid. This can be made to produce steam. - This is a renewable energy resource because heat is always present in the Earth's crust. - **Pros:** The ground stays a relatively constant temperature and heat is supplied by the Earth. Can also use for cooling. - **Cons:** Very expensive to install ## BIOMASS GENERATION - This is any form of plant or animal matter, including wood, straw, manure, plant-based oils, and decaying natural materials. - It also includes biodegradable wastes. - This is a renewable energy resource because it uses organic matter which grows on Earth and can replace itself. - **Pros:** Organic material is available everywhere - **Cons:** Creates methane and CO2, which are greenhouse gases. ## GENERATING USING NON-RENEWABLE SOURCES This form of energy is obtained by using the Earth's resources where they will eventually run out and will take too long to replace. They also pollute. They all use thermal generation. ## THERMAL GENERATION All these non-renewable sources use heat to produce electricity. In all cases, this involves heating water to produce steam. The steam pressure is then used to turn a turbine to generate electricity. ### FOSSIL FUELS Coal, oil and natural gas can be used to create significant amounts of heat. - **Pros:** these processes release a large amount of energy. - **Cons:** Burning produces CO2 which can contribute to global warming. Burning also can release other toxic gases which contribute to acid rain. ### NUCLEAR POWER - Taking uranium atoms and smashing apart their nuclei is the process used in nuclear reactors. This creates tremendous amounts of heat. - **Pros:** Provides huge amount of energy, doesn't make greenhouse gases. - **Cons:** Nuclear waste must also be stored and this radioactivity raises enormous environmental concerns. ## ELECTRICAL POWER and EFFICIENCY Electrical power (P) is the rate at which electrical energy is produced or consumed in a given time. The unit of measurement for electrical power is the watt (W). A 60W incandescent bulb, a 18 W compact fluorescent bulb (CFL) and an 10W LED bulb produce about the same amount of light (measured in lumens). The 60W bulb, however, generates 45W of heat (only 15W is used for light), which makes it an inefficient use of lighting your home. Notice how little energy an LED uses for roughly the same amount of light, and how long they last. - A watt-hour means that one watt of energy is constantly used for one hour - A kilowatt-hour means that one thousand watts of energy is constantly used for one hour. Our electric bill charges us by the kilowatt-hour, and this is written: kWoh ### EFFICIENT DEVICES Not all electrical devices use electrical energy efficiently. - **Efficiency** is a measure of how much useful energy an electrical device produces compared with the amount of energy that was supplied to the device. - Some older appliances are less efficient at doing the same task. For example, old clothes dryers might have used 800 kilowatt-hours (kWh) of energy in one year, but the newer ones only use up 300 kW.h. They perform the same task, but one uses less energy because it's more efficient. - Efficiency must be lower than 100% because when converting one form of energy to another, energy is lost in the process (however large or small that might be) due to friction, etc. ## COST OF ELECTRICITY In Ontario, the price of electrical energy changes depending on the time of day, and which day of the week it is. - It is most expensive on weekdays from 7 AM to 7 PM. - The prices per kWh varies a bit by region, but generally off-peak prices are about half of the on-peak prices. The cost of operating an electrical device can be calculated using the equation: **COST TO OPERATE = power used (kW) x time (hours) x cost of electricity.** *Example:* A 60 W light bulb is left on 8 hours per day for 1 year. Electricity costs 8.2 ¢/kW-h. - Calculate the cost to operate the light bulb. - First, convert W to kW (divide by 1000) so 60W = 0.06 kW. Also find the total hours (x 365). - Cost = 0.06 kW x (8 x 365) x 8.2 = 1436.6 cents, or $14.37 for the whole year.