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# Per14_over - Preview of Period 14: Electrical Safety and...

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Preview of Period 14: Electrical Safety and Transmission 14.1 Fuses and Circuit Breakers How do fuses and circuit breakers prevent fires? 14.2 Preventing Electric Shock What safety devices prevent electric shock? 14.3 Transmitting Electricity with Transformers How can we efficiently and safely transmit electricity from generating plants to consumers? 14.4 Transformers How do transformers trade voltage and current in a circuit? 14-1

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Joule Heating Joule heating occurs when a resistor is heated as current flows through it. P joule = I 2 R P joule = power (in watts) I = current (in amps) R = resistance (in ohms) The larger the current, the greater the joule heating. If the current is large enough, joule heating can start a fire. A large current occurs when the resistance of the circuit is decreased. The circuit resistance decreases as more appliances are connected in parallel. A short circuit lowers the circuit resistance by providing a low resistance path for current 14-2
Open, Closed, and Short Circuits Closed Circuit Open Circuit With a closed circuit With an open circuit the bulb lights. the bulb does not light . Short Circuit With a short circuit bulb does not light because the current follows a path with less resistance that bypasses the bulb. 14-3

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Devices to Prevent Electrical Fires: Fuses and Circuit Breakers Fuses: If a dangerously large current flows through a circuit, the fuse melts and opens the circuit. Circuit Breakers: A circuit breaker switches opens the circuit if the circuit resistance is lowered and a dangerously large current flows. 14-4
Avoiding Electrical Accidents Preventing Electrical Fires Don’t lay electric cords under carpeting. Keep cords away from water and heat. Disconnect appliances by pulling on the plug, not on the cord. Replace worn cords. Never break off the third safety prong on a plug. Use an adapter. If a switch or an outlet becomes warm, replace it

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## This note was uploaded on 06/11/2011 for the course PHYSICS 103 taught by Professor Staff during the Spring '10 term at Ohio State.

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Per14_over - Preview of Period 14: Electrical Safety and...

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