PHYSICS 241

PHYSICS 241 - Physics 241 Lecture 10 Y. E. Kim September...

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Physics 241 Lecture 10 Y. E. Kim September 23, 2010 Chapter 25, Sections 1 - 5 September 23, 2010 University Physics, Chapter 25 1
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September 23, 2010 University Physics, Chapter 25 2 Direct Current ± We will study charges in motion ± Electric charge moving coherently from one region to another is called electric current ± Current is flowing through light bulbs, iPods, and lightning strikes ± Current usually consists of mobile electrons traveling in conducting materials ± Direct current is defined as a current that flows only in one direction in the conductor Most of our electric technology is based on Alternating Current ± Chapter 26 Computers, electronic devices are based on direct currents.
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September 23, 2010 University Physics, Chapter 25 3 Electric Current (1) ± We define the electric current i as the net charge passing a given point in a given time ± Random motion of electrons in conductors, or the flows of electrically neutral atoms, are not electric currents in spite of the fact that large amounts of charge are moving past a given point ± If net charge dq passes a point in time d t we define the current to be
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September 23, 2010 University Physics, Chapter 25 4 Electric Current (2) ± The amount of charge q passing a given point in time t is the integral of the current with respect to time given by ± Charge conservationimplies that charge flowing in a conductor is never lost ± Therefore the same amount of charge must flow into one end of the conductor and exit from the other end of the conductor 0 dq id ³³
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September 23, 2010 University Physics, Chapter 25 5 The Ampere ± The unit of current is coulombs per second, which has been given the unit ampere, named after French physicist André- Marie Ampère, (1775-1836) ± The ampere is abbreviated as A and is defined by ± Some typical currents are ± Flashlight - 1 A ± The starter motor in a car - 200 A ± iPod - 50 mA ± Lightning strike (for a very short time) ² 100,000 A 1 C 1 A 1 s
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September 23, 2010 University Physics, Chapter 25 6 Batteries ± We use batteries as devices that provide direct currents in circuits ± The voltage written on it is the potential difference that it can provide to a circuit ± You will also find its rating in units of mAh ± This rating provides information on the total charge that a single battery can deliver over its lifetime ± The quantity mAh is another unit of charge: 1 mAh (10 ± 3 A)(3600 s) 3.6 As 3.6 C
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September 23, 2010 University Physics, Chapter 25 7 In this circuit, electrons flow around the circuit counterclockwise. (The conventionally defined current is clockwise; remember, electrons are negative charges.) The electrons FDQ·W GLVDSSHDU VR WKH FXUUHQW requires a whole loop! Chemical action pumps electrons from the positive terminal (+) to the negative terminal ( - ) in the battery.
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PHYSICS 241 - Physics 241 Lecture 10 Y. E. Kim September...

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