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Science 9 Unit D Booklet 2Modeling and Measuring ElectricityIn your notes, write how currents can be compared to a Waterfall. Write how water flow can be used to describe resistanceThere are many types of resistors for different things ex. Electronics in a TVThe most common types of resistors are wire-wound and carbon-composition. They vary from 0.1 Ω to 200 kΩFactors that Affect ResistanceFactorEffect1234Measuring ElectricityMeasurementUnitMeasured Using12What can a Galvanometer be used for?Voltage is also called _______________________________. It is named after Alessandro Volta.Some common voltagesFlashlights- 6 V or lessCar Batteries- 12 VWall Sockets- 120 VMajor Power Lines- 100 kVDemo:How Many Volts are there in a…D BatteryAA BatteryNotes- when using a voltmeter you must attach the red terminal to the positive side of the battery and attach the black side to the negative side of the batterOhms LawGeorge Simon Ohm experimented with different substances, and found a relationship between He found that if the temperature remained the same when1) The resistance of a conductor stays constant2) Current is directly proportional to the voltage appliedSo… if you increase the voltage, you increase the current too and vice versaThe Formula for Ohms law is ___________________________________________________V= voltage volts (V) (voltmeter)I= current amps (A) (ammeter)R= resistance ohms (Ω) – (ohmmeter)Steps to Solving Ohms Law Problems1) Identify the known quantities2) Identify the unknown quantities3) Rearrange the formula if necessary4) Fill in the numbers for the variable and solveExamplesA motor has an internal resistance of 40 Ω. The motor is in a circuit with a current of 4.0 A. What is the voltage? A 30 V battery creates a current through a 15 Ω resistor. How much current is created?An electric stove is connected to a 240 V outlet. If the current flowing through the stove is 20 A, what is the resistance of the heating element?A hair dryer takes 1200 mA to run and it gives a resistance of 40 Ω. What voltage is necessary?Please complete the last page of the booklet – this will be markedEnergy Forms and TransformationsThink about it! What types of energy do we know of?TypeDefinition3 ExamplesChemical EnergyElectrical EnergyMechanical Energy Thermal EnergyEnergy TransformationsThere are many ways to convert energy forms into the other formsUsing this table, come up with devices that you use every day that follow the same energy transformationTake a Break! Read the paragraphs below0000What is a thermocouple?When is a thermocouple useful?What energy conversions do thermocouples do?What energy conversion to heaters and ovens do?Energy Transformations Involving Electrical and Mechanical EnergyIn 1820 Hans Christian Oersted discovered that a wire with a current running through it created a magnetic field. Michael Faraday used the connection between electricity and magnetism to make the first motor in 1831However, he used an open container or mercury in his design. Why wouldn’t we used that today?ElectromagnetsAn electromagnet is only a magnet when __________________________________________________ It is possible to change the poles of the electromagnet by ______________________________________________________________________________How is that different from a permanent magnet?An electromagnet will line up in a magnetic field made from permanent magnetsParts of an Electromagnetic Motor:A commutator and brushes are used to reverse the flow of electricity through the The commutator is a The armature keeps spinning during that time because of momentumThe commutator keeps spinning and reconnects to There brushes touch the commutator 4504055222359000-15240-2921000DC ElectromotorDC Electric GeneratorDirect and Alternating CurrentDirect current (DC) only flows:Many devices such as cell phones and computers use DCAlternating current (AC) flows:AC current flows into your houseDevices that need DC often come with their own power supplyTransformersPower companies use AC because it can be transformed into different voltages without energy loss. Power comes from generating stations at a _______________________________ and is transformed to a _________________________ through a _________________________________GeneratorsMichael Faraday also discovered that he could create an electrical current by moving a wire through a magnetic field (the motion created the electricity)A hand-held generator moves a coil of wire in ________________________________________The faster you turn the _______________________________________Most electric power stations use generatorsGenerators are:How would hydroelectric dams use a generator?How would a wind turbine use a generator?How would a coal burning plant use a generator?Measuring Energy Input and Output Power is the rate __________________________________________________________Measured in watts which is equal to J/s. The Formula is:P= power (watts)I= current (amps)V= voltage (volts)Solving Power Problems1) Identify known quantities2) Identify unknown quantities3) Rearrange the formula if necessary4) Fill in the numbers and solve the problemExample 1: If a blender uses 40 V when there is a current of 3.4 A, what power did it use?Example 2: A hair dryer has a power rating of 1000 W. It is plugged into a 120 V outlet. What is the current flowing through the hair dryer?EnergyIn order to discover how much energy a device uses we need to know how long it uses power forThe Formula for Energy is:E= energy (Joules- J)P= power (W)t= time (seconds)Steps for solving Energy Problems:1) Identify known quantities2) Identify unknown quantities3) Rearrange the formula if necessary4) Fill in the numbers and solve the problemA microwave oven has power rating of 800 W. If you cook a roast in this oven for 30 minutes on high, how many Joules of electrical energy are converted by the microwave?If 6200 kJ of energy are used to run a TV for a week and the power rating of a TV is 300 W, how many seconds, minutes and hours was the TV on for?A kilowatt hour is the unit used to measure how much energy households or businesses use- usually in a hour and then have to pay forTo find kilowatt hours you use the same formulaE(kWh)= P(kW) x t(h) but use kilowatt instead of watts and hours instead of secondsA microwave oven has a power rating of 800 W. If you cook a roast in this oven for 30 minutes on high, how many kilowatt hours did it use during that time?A CFL light bulb that uses 25 watts of power is used for 125 hours. It costs 15 cents/kWh to run one light bulb. Calculate the kilowatt hours that the light bulb uses, then calculate how much it will cost to run the light bulb.Energy DissipationThe Law of Conservation of Energy says: However, the output energy of an energy transformer is always less than its inputWhere does the energy go? You create an electric pump with a motor to pump water from an irrigation ditch to irrigate a crop. You find that the motor used 100 kJ of electrical energy for every 75 kJ of work done rating water to the field. Where did the other 25kJ go?EfficiencyThe efficiency of a device is a ratio of:The more useful energy that comes out the more efficient the device isWe use percent efficiencyExample:Calculate the percent efficiency of an incandescent light bulb that produces 2 500 J of light energy from 50 000 J of electrical energy.We can compare efficiencies of devices which will tell us about their energy cost and their environmental impactNew technologies often help make devices more environmentally friendly and make them more efficientUnit D Assignment – Calculations for Electricity – HAND IN! This is for Marks!Name:_________________________How much current is created if a 12 V battery passes current through a 10 Ohm resistor?An electric shaver that is plugged into a 110 V wall outlet has a resistance of 6,000 Ohms. How much current flows through this device?An electric garage heater draws 30 A from a special 220 V circuit designed for heavy duty heaters. What is the heaters resistance?An electric drill draws 3.2 amps of electric current at 120 volts. What is the power output of this drill?An aquarium light bulb uses 210 J of energy in 30 s. How much power does it use? How many joules of energy would be used by a 60-W light bulb in 1 hour? Determine the percent efficiency of a 60 W fluorescent light bulb that uses 2000J of electrical energy to produce 400J of light energy. Calculate the percent efficiency of an electric motor that uses 15 000 J of energy to produce 11 500 J of useful energy A washing machine has a power-rating of 2500W. If a unit of electricity costs 24 cents per hour, how much does it cost to run the appliance for 90 minutes? ................
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