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Review18

# Review18 - Section 18.1 Sources of emf Any device such as a...

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Section 18.1: Sources of emf Any device, such as a battery or generator, that increases the electric potential energy of charges in an electric circuit is called a source of emf . Batteries convert chemical energy into electrical potential energy, and generators convert mechanical energy into electrical potential energy. We can treat a battery as an “internal resistance” in series with the emf, but we usually can ignore the internal resistance. Section 18.2: Resistors in Series The equivalent resistance of a set of resistors connected in series is + + + = 3 2 1 R R R R eq [18.4] The current is the same through each resistor in series, and is the same as the current through the equivalent resistance. The voltages across the individual resistors add to give the voltage across the equivalent resistance. Section 18.3: Resistors in Parallel The equivalent resistance of a set of resistors connected in parallel is " + + + = 3 2 1 1 1 1 1 R R R R eq [18.6] The potential difference across any two parallel resistors is the same. The currents through each

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