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PH 122 (46)

Energy and power, Kirchhoff's Laws, reducing complex circuits

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PH 122
Brian Jones

14 February A power and resistance puzzle A 60 W and a 100 W bulb are connected in series. Think about the current in the circuit, and through each bulb. Which bulb has higher resistance? 100 W Energy and power The energy used by a circuit is supplied by the emf of the battery through a series of energy transformations E chem(chemical energy in the battery) → elecpotential energy of separated charges) → K (kinetic energy of moving charges) → E (thermal energy of atoms in the resistor) The battery supplies power at the rate P = Iε emf 2 2 (∆V )R The resistor dissipates power at the rateRP = IΔR = I R = R Warming Up: What’s the voltage output of your stereo? Suppose a stereo speaker (with a resistance of 8 Ω) uses a power of 20 watts. What is the voltage across the speaker? 2 (∆V R ) P = R PR = V 2 V = √PR V = √8x20 V = √160 Adding Voltages in Series An electric eel may have 6,000 electrolytes connected in series. Each can produce a voltage of 150 mV. What total voltage could the
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