Notes on Chapter 27

# Notes on Chapter 27 - Chapter 27 Circuits 27-1 What is...

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24 June 2010 1 Chapter 27 - Circuits Every electrical device you come in contact with as well as the power grid supplying electricity for the country depends on electrical/electronic engineering (and electric circuits in order to operate) 27-1 What is Physics?

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24 June 2010 2 “Pumping” Charge An emf device does work on the charge carriers in order to maintain the potential difference . A good analogy is a water pump which maintains the flow of water through the pipe as a result of the pressure difference Pump Valve emf device 27.2
24 June 2010 3 An emf device provides an electromotive force (an old-fashioned word) Examples of emf devices are: Battery (conversion of chemical energy) Electric generator (conversion of mechanical energy) Solar cells (conversion of thermal energy) Thermopile (temperature difference) Fuel cell (conversion of chemical energy )

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24 June 2010 4 Work, Energy and Emf Within the emf device positive charge carriers flow from low potential (-) to high potential (+), hence doing work on the positive charges. Note the arrow indicating the direction of the emf 27.3 dW dq = E The emf, E of an emf device is the work done per unit charge that the device does to move charge from low the potential to the high potential terminal SI unit of E is the volt : 1 volt = 1 J/C
24 June 2010 5 Mechanical analog of a circuit consisting of a resistance and a source of emf

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24 June 2010 6 Ideal emf device has no internal resistance the potential difference between the terminals = E Real emf device has an internal resistance the potential difference between the terminals only if the device is not connected to a circuit = E
24 June 2010 7 Battery B is discharging while charging battery A and provides energy for motor M and thermal energy in resistance R Consider a circuit consisting of A and B which are rechargeable batteries a resistor of resistance R , M is an electric motor that can lift the object of mass m ( determines the direction of the net current i ) > BA EE

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24 June 2010 8 Current in a Single-Loop Circuits
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Notes on Chapter 27 - Chapter 27 Circuits 27-1 What is...

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