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Lecture 5

# Lecture 5 - ENGR 111 Lecture 5 Reading Class notes Review...

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ENGR 111 Lecture 5 Reading: Chapters 19, 20 Class notes

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Fall 2004 Review of Last Class l Ohm’s Law V = I * R l KCL/KVL and Ohm’s law allow us to compute equivalent resistances l Resistances in series R = R1 + R2 l Resistances in parallel 1/R = 1/R1 + 1/R2 l Resistances in series => Voltage Dividers l Resistances in parallel => Current dividers
Fall 2004 Power l Power = rate at which energy consumed or produced l Power, symbol (P), Units (Watts) l P = I * V l Water analogy, amount of water (current), the height of the drop (voltage) determine power l Horsepower ratings on engines, wattage ratings on bulbs

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Fall 2004 Energy l Charge moving through battery converts chemical energy to electrical energy l Energy U = Q V = (charge * Voltage) l Energy units (Joules, KWh), symbol (U) l Remember Power = rate of energy consumed = dU/dt = d/dt (QV) = dQ/dt V = I V l Utility bill in KWh = 1000 Watts over an hour = 1000 Watts * 3600 sec = 3.6 MJoules
Fall 2004 Energy l Energy use of increasing importance l So many electrical gadgets, computers, networks, phones, cell phones, … l Portable devices laptops, cell phones should run for long periods after charging l Environmental concerns, power scarcity

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Lecture 5 - ENGR 111 Lecture 5 Reading Class notes Review...

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