lecture 7

lecture 7 - 20.4 Electrical Power Our standard definition...

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20.4 Electrical Power Our standard definition of power is: . ime Work Power = Time So what would electrical power be? From the definition of potential: qV W q W V = = V Thus, t qV P = IV P = We can write this different ways using Ohm’s Law, V=IR : V P R I P 2 2 = = R *So we have 3 ways of calculating electrical power epending on what other quantities are known depending on what other quantities are known.
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Electrical Energy Work and Energy have the same units (Joules). Thus, Time Power Energy × = Electrical companies, like Entergy, measure your monthly energy use this way, in units of kilowatt hours (kWh). For example, if you used an average power of 1500 W for 31 days (744 hours), your energy consumption would be: Wh 116 44 W kWh 1116 ) h 744 )( kW 5 . 1 ( = = E At a cost of roughly $0.13/kWh, this would be a monthly bill of $145. J 10 60 . 3 kWh 1 6 × =
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Power Transmission Why is the electrical power transmitted at high voltages, instead of high currents??? Thermal losses (losing electrical power by converting it to heat) is proportional to I 2 for a given voltage and proportional to V .
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This note was uploaded on 08/04/2009 for the course PHYS 2002 taught by Professor Blackmon during the Spring '08 term at LSU.

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lecture 7 - 20.4 Electrical Power Our standard definition...

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