8B - 10_AC__11

8B - 10_AC__11 - Alternating Currents - AC The electricity...

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Alternating Currents - AC The electricity supplied by power companies is alternating. The voltage varies + to - sinusoidally (60 cycles per sec in USA). AC is used because it can be transformed to high V and transmitted over long distances efficiently. (Lower i 2 R losses) The main uses are: 1) power - for lighting, machinery, etc. 2) electronics - computers, TV, radio, etc
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Alternating Current Generator The basic mechanism of an alternating-current generator is a conducting loop rotated in an external magnetic field. In practice, the alternating emf induced in a coil of many turns of wire is made accessible by means of slip rings attached to the rotating loop. Each ring is connected to one end of the loop wire and is electrically connected to the rest of the generator circuit by a conducting brush against which the ring slips as the loop and ring rotate.
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Compared to DC Generator DC generator has split-rings, so direction of current to a given brush is always the same.
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DC has same direction of i The current is in one direction in a DC generator, but varies in amplitude. Can use L and C to smooth out the variations and get a fairly constant V.
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Use of AC for power
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Power Delivered in AC P avg = I 2 R/2 = ( I / ˽± ) 2 R I rms = I / ˽± = rms current Over a cycle, average of sin 2 ! = 1/2
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Electricity sources and uses in USA Energy converted to electricity = 36%. Transmission loss = 7%. Source: EIA
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This note was uploaded on 04/10/2011 for the course PHYS 8B taught by Professor Catherinebordel during the Spring '10 term at Berkeley.

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8B - 10_AC__11 - Alternating Currents - AC The electricity...

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