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Principles of Technology Work in the Electrical System Work in the Electrical System 1. What is the charge on a proton? - positive 2. What is the charge on an electron? - negative Work in the Electrical System 3. What is electrical current? - flow of electrons through conductors 4. How do electrons flow in a DC circuit? - electrons flow the negative terminal through the conductors to the positive terminal Work in the Electrical System 5. How do we measure electric charge? - coulombs (q) - one coulomb is equal to 6.25 x 1018 electrons Work in the Electrical System 6. How do we calculate electrical work? - Work = Voltage Difference x Charge moved -W=Vxq 7. What is the unit for electrical work? - Joules (volt-coulombs) Work in the Electrical System 8. Can batteries be recharged? - some can, but it takes electrical work to do so - to recharge a battery, electrical current flows through the battery opposite from the way it discharge current Work in the Electrical System 9. Example – A dead 12 V battery can store 8000 coulombs of electrical charge. How much electrical work is done to recharge the battery if a voltage difference of 12 V is applied? Work in the Electrical System - Work = voltage difference x charge - work = 12 V x 8000 coulombs - work = 96,000 joules Work in the Electrical System 10. How are electrical current and charge related? - while coulombs cannot be easily measured, the rate at which coulombs move (aka current) can be 11. How is current measured? - amperes (I) Work in the Electrical System 12. What is the equation for current? - Current = Charge Time - I = q (or q = I x t) t Work in the Electrical System 13. What is the equation for charge from current? - charge = current x time - q = I x t, where - q coulombs - I amperes - t seconds Work in the Electrical System 14. Example – A DC electric motor operates for two minutes on a voltage of 12 volts while drawing a current of 4 amperes. How much electrical work is done? Work in the Electrical System 1. Find q first -q=Ixt - q = (4 A) x (120 sec) - q = 480 coulombs 2. Solve for work -w=Vxq - w = 12V x 480 C - w = 5760 J Work in the Electrical System 15. What are effects of electrical work? - you cannot see electrical work, only the effects of it - electrical work produces movement, heat, light, or sound Work in the Electrical System 16. What are some examples of how work causes movement? - electrical motors or switches Work in the Electrical System 17. What are some examples of how work causes heat? - heaters, dryers, ovens, light bulbs, motors 18. What are some examples of how work causes light? - flashlights, lamps, radio waves, microwaves, cell phone signals Work in the Electrical System 19. What are some examples of how work causes sound? - speakers, TVs, PA systems, alarm clocks 20. What is electrical efficiency? - ratio of useful work done (output) to the required electrical input Work in the Electrical System 21. What is the equation for efficiency of an electrical device? - Eff = W out x 100% W in - W out = work done by device - W in = electrical energy required Work in the Electrical System 22. Example – A crane lifts an I-beam a height of 2.5 meters. The I-beam weighs 2000 N. The crane requires an input of 5760 J. What is the efficiency of the crane? Work in the Electrical System 1. Find the work done -W=FxD - W = 2000 N x 2.5 meters - W = 5000 J Work in the Electrical System 2. Find the efficiency -Eff = W out x 100% W in - Eff = 5000 J x 100% 5760 J - Eff = 86.8 % Work in the Electrical System 23. How is electricity produced? - coal, gas, or oil is burned to produce heat energy - the heat energy is used to convert water into steam - steam pressure is used to drive turbines - turbines drive electrical generators to produce electricity Work in the Electrical System 24. Why use electricity? - easy to transport over long distances through wires - clean – no by products - convenient and easy to use; provides a ready source of energy when you want it - operates many machines and electronic devices