E13_03-01-10 - E13: Practical Electricity A. Parallel and...

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E13: Practical Electricity A. Parallel and Series Circuits 1. Christmas mini lights i) Typically strings of 50, 100, or 150 bulbs ii) Uses 2.5 V incandescent bulbs iii) 50 bulbs wired in series (why don’t they all go out when one burns out?) 2. 3-way bulbs (50W-100W-150W, for example) i) Two filaments wired in parallel ii) How does it supply three different brightnesses? iii) Which filament has the higher resistance (50W or 100W)? 3. House wiring i) Two lamps are plugged into the two receptacles of one outlet. Are they wired in parallel or series? ii) Circuit breakers limit current in one circuit to 15 or 20 amps. iii) Most modern houses can supply up to 200 amperes total. iv) Why are there three electrical wires coming from the street to the house? Plus cable and telephone lines. B. Human response to electricity 1. Typical resistance i) Dry skin – about 100,000 ohms or more ii) Wet skin – about 1000 ohms iii) Through body between perspiring hands – about 1500 ohms iv) With 120 volts AC, current through dry skin I = 120 V/100,000 ohm =
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E13_03-01-10 - E13: Practical Electricity A. Parallel and...

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