Generators supply electrical energy.

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1 Page of 5 KY CONCPT Generators supply electrical energy. BFOR, you learned Magnetism is a force exerted by magnets A moving magnetic field can generate an electric current in a conductor Generators use magnetism to produce current NOW, you will learn How power plants generate electrical energy How electric power is measured How energy usage is calculated VOCABULARY electric power p. 0 watt p. 04 kilowatt p. 04 kilowatt-hour p. 05 THINK ABOUT How can falling water generate electrical energy? This photograph shows the Hoover Dam on the Nevada/Arizona border, which holds back a large lake, almost 600 feet deep, on the Colorado River. It took thousands of workers nearly five years to build the dam, and it cost millions of dollars. One of the main purposes of the Hoover Dam is the generation of current. Think about what you have read about generators. How could the energy of falling water be used to generate current? VOCABULARY Use a description wheel to take notes about electrical power. Generators provide most of the world s electrical energy. The tremendous energy produced by falling water provides the turning motion for large generators at a power plant. The power plant at the Hoover Dam supplies energy to more than a million people. Other sources of energy at power plants include steam from burning fossil fuels, nuclear reactions, wind, solar heating, and ocean tides. ach source provides the energy of motion to the generators, producing electrical energy. lectric power is the rate at which electrical energy is generated from another source of energy. Check Your Reading What do power plants that use water, steam, and wind all have in common? 0 Unit: lectricity and Magnetism

2 Page of 5 Generating lectrical nergy How does the power plant convert the energy of motion into electrical energy? Very large generators in the plant hold powerful electromagnets surrounded by massive coils of copper wire. The illustration below shows how the energy from water falling from the reservoir to the river far below a dam is converted to electrical energy. As the water falls from the reservoir, its kinetic energy increases and it flows very fast. The falling stream of water turns a fan-like device, called a turbine, which is connected to the generator s shaft. The rotation of the shaft turns powerful electromagnets that are surrounded by the coil of copper wires. The coil is connected to a step-up transformer that sends high-voltage current to power lines. Far from the plant, step-down transformers reduce the voltage so that current can be sent through smaller lines to neighborhoods. Another transformer reduces the voltage to the level needed to operate lights and appliances. RSOURC CNTR CLASSZON.COM Find out more about dams that generate current. How lectrical Power Is Generated Power plants use generators to convert kinetic energy into electrical energy. step-up transformers step-down transformers shaft turbine Falling water provides energy to turn the turbine of the generator. The shaft turns a powerful electromagnet within a coil of wire, generating electrical current. Current is sent along power lines at a high voltage. The voltage level is adjusted by transformers. How is kinetic energy turned into electrical energy in a Reading power plant? visuals question Chapter : Magnetism 0

3 Page of 5 RSOURC CNTR CLASSZON.COM Learn more about energy use and conservation. lectric power can be measured. You have read that electric power is the rate at which electrical energy is generated from another source of energy. Power also refers to the rate at which an appliance converts electrical energy back into another form of energy, such as light, heat, or sound. In order to provide electrical energy to homes and factories, power companies need to know the rate at which energy is needed. Power can be measured so that companies can determine how much energy is used and where it is used. This information is used to figure out how much to charge customers, and it is used to determine whether more electrical energy needs to be generated. To provide energy to an average home, a power plant needs to burn about four tons of coal each year. Typical Power Ratings Appliance Watts and Kilowatts Watts DVD player 0 Radio 0 Video game system 5 lectric blanket 60 Light bulb 75 Stereo system 00 Window fan 00 Television 0 Computer 0 Computer monitor 50 Refrigerator 700 Air conditioner 000 Microwave oven 000 Hair dryer 00 Clothes dryer 000 The unit of measurement for power is the watt (W). Watts measure the rate at which energy is used by an electrical appliance. For instance, a light bulb converts energy to light and heat. The power rating of the bulb, or of any device that consumes electrical energy, depends on both the voltage and the current. The formula for finding power, in watts, from voltage and current, is shown below. The letter I stands for current. lectrical Power VoltagepCurrent P VpI You have probably seen the label on a light bulb that gives its power rating in watts usually in the range of 40 W to 00 W. A brighter bulb converts energy at a higher rate than one with a lower power rating. The chart at the left shows typical power ratings, in watts, for some appliances that you might have in your home. The exact power rating depends on how each brand of appliance uses energy. You can find the actual power rating for an appliance on its label. The combined power rating in a building is likely to be a fairly large number. A kilowatt (kw) is a unit of power equal to one thousand watts. All of the appliances in a room may have a combined power rating of several kilowatts, but all appliances are not in use all of the time. That is why energy is usually calculated based on how long the appliances are in use. check your reading xplain what kilowatts are used to measure. 04 Unit: lectricity and Magnetism

4 Page 4 of 5 Power How would you use your electrical energy? PROCDUR On a sheet of graph paper, outline a box that is 0 squares long by 8 squares wide. The box represents a room that is wired to power a total of 800 W. ach square represents 0 W of power. From the chart on page 04, choose appliances that you want in your room. Using colored pencils, fill in the appropriate number of boxes for each appliance. All of the items that you choose must fit within the total power available, represented by the 80 squares. SKILL FOCUS Making models MATRIALS graph paper colored pencils TIM 0 minutes WHAT DO YOU THINK? How did you decide to use your electrical energy? Could you provide enough energy to operate everything you wanted at one time? CHALLNG During the summer, power companies sometimes cannot produce enough energy for the demand. Why do you think that happens? Calculating nergy Use The electric bill for your energy usage is calculated based on the rate at which energy is used, or the power, and the amount of time it is used at that rate. Total energy used by an appliance is determined by multiplying its power consumption by the amount of time that it is used. nergy used Powerptime Ppt The kilowatt-hour is the unit of measurement for energy usage. A kilowatt-hour (kwh) is equal to one kilowatt of power for a one-hour period. Buildings usually have meters that measure how many kilowatthours of energy have been used. The meters display four or five small dials in a row, as shown in the photograph on the right. ach dial represents a different place value ones, tens, hundreds, or thousands. For example, the meter in the photograph shows that the customer has used close to 9,000 kwh of energy 8,9 kwh, to be exact. To find how much energy was used in one month, the last month s reading is subtracted from this total. Chapter : Magnetism 05

5 Page 5 of 5 To determine the number of kilowatt-hours of energy used by an appliance, find its wattage on the chart on the page 04 or from the label. Then, substitute it into the formula along with the number of hours it was in use. Solve the sample problems below. Finding nergy Used Sample Problem How much energy is used to dry clothes in a kw dryer for 0 minutes? What do you know? What do you want to find out? Write the formula: Substitute into the formula: Calculate and simplify: Check that your units agree: Power.0 kw, time 0.5 hr nergy used Pp t.0 kwp 0.5 hr.5 kwh Unit is kwh. Unit for energy used is kwh. Units agree. Practice the Math Answer:.5 kwh. All of the appliances in a computer lab are in use for 6 hours every day and together use. kw. How much energy has been used in day?. How much energy is used when a. kw hair dyer is in use for 0. hr? nergy prices vary, but you can estimate the cost of using an electrical appliance by using a value of about 8 cents/kwh. You can calculate how much energy you can save by turning off the lights or television when you are not using them. Although the number may seem small, try multiplying your savings over the course of a month or year. KY CONCPTS. How do power plants generate electrical energy from kinetic energy?. xplain what watts measure.. How is energy use determined? CRITICAL THINKING 4. Apply Think about reducing energy usage in your home. What changes would make the largest difference in the amount of energy used? 5. Calculate How much energy is used if a 000 W clothes dryer is used for 4 hours? CHALLNG 6. Calculate An electric bill for an apartment shows 96 kwh of energy used over one month. The appliances in the apartment have a total power rating of. kw. How many hours were the appliances in use? 06 Unit: lectricity and Magnetism