chapter25notes - Chapter 25 Electric Potential Electric...

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Unformatted text preview: Chapter 25 Electric Potential Electric Potential and Potential Energy Electric Potential and Potential Energy Electric Potential and Potential Energy Electric Potential and Potential Energy Electric Potential and Potential Energy Electric Potential and Potential Energy What is the definition of the electric potential? The potential energy difference per unit charge So based on this, how differently would you describe the electric potential in words? A measure of how much energy an electric charge can acquire in a given situation A measure of how much work a given charge can do. Electric Potential and Potential Energy Comparisons of Potential Energies Lets compare gravitational and electric potential energies 2m m What are the potential energies of the rocks? mgh and 2mgh Which rock has a bigger potential energy? The rock with a larger mass Why? Its got a bigger mass. What are the potential energies of the charges? QV ba and 2QV ba Which object has a bigger potential energy? The object with a larger charge. Why? Its got a bigger charge. The potential is the same but the heavier rock or larger charge can do a greater work. Electric Potential and Potential Energy The electric potential difference gives potential energy or possibility to do work based on the charge of the object. So what is happening in batteries or generators? They maintain a potential difference. The actual amount of energy used or transformed depends on how much charge flows. How much is the potential difference maintained by a cars battery? 12Volts If for a given period, 5C charge flows through the headlight lamp, what is the total energy transformed? E tot =5C*12V=60 Umm What is the unit? If it is left on twice as long? E tot =10C*12V=120J. Joules Some Typical Voltages 10-4 V Potential changes on skin (EKG and EEG) 10-1 V Resting potential across nerve membrane 1.5 V Flashlight battery 12 V Automobile battery 10 2 V Household outlet 10 4 V Automobile ignition 10 4 V Power supply for TV tube 10 6 V High-Voltage Power Lines 10 8 V Thundercloud to ground Approximate Voltage Sources Example 1 Electrons in TV tube: Suppose an electron in the picture tube of a television set is accelerated from rest through a potential difference V ba =+5000V. (a) What is the change in potential energy of the electron? (b) What is the speed of the electron (m=9.1x10-31 kg) as a result of this acceleration? (c) Repeat for a proton (m=1.67x10-27 kg) that accelerates through a potential difference of V ba =-5000V. (a) What is the charge of an electron? So what is the change of its potential energy?...
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This note was uploaded on 11/01/2009 for the course PHY phy2049 taught by Professor Wilfredngwa during the Fall '09 term at University of Central Florida.

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chapter25notes - Chapter 25 Electric Potential Electric...

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