Phys2212_29.5+to+29.7

Phys2212_29.5+to+29.7 - Physics 2212 Electricity and...

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Unformatted text preview: Physics 2212 Electricity and Magnetism Lecture 11 (Knight: 29.5 to 29.7) Electric Potential, Equipotential Surfaces and E = - r V 10/06/09 Physics 2212 - Lecture 11 2 The Electric Potential In Chapter 25 we introduced the concept of an electric field E , which can be though of as a normalized force, i.e., E = F/ q , the field E that would produce a force F on some test charge q . We can similarly define the electric potential V as a charge-normalized potential energy, i.e., V=U elec /q , the electric potential V that would give a test charge q an electric potential energy U elec because it is in the field of some other source charges. We define the unit of electric potential as the volt : 1 volt = 1 V = 1 J/C = 1 Nm/C. Other units are: kV=10 3 V, mV=10-3 V, and V=10-6 V. Example: A D-cell battery has a potential of 1.5 V between its terminals. 10/06/09 Physics 2212 - Lecture 11 3 What Good is the Electric Potential? Like the electric field E , the electric potential V is an abstract idea. It offers an advantage, however, because it is a scalar quantity while E is a vector, yet the two can be converted to each other. It is useful because: l The electric potential V depends only on the charges and their geometries. The electric potential is the ability of the source charges to have an interaction if a charge q shows up. The potential is present in all space, whether or not a charge is there to experience it. l If we know the electric potential V throughout a region of space, well immediately know the potential energy U = qV of any charge q that enters that region. Losing Potential Energy Gaining Kinetic Energy Gaining Potential Energy Losing Kinetic Energy 10/06/09 Physics 2212 - Lecture 11 4 Example : Moving Through a Potential Difference A proton with a speed of v i = 2.0 x 10 5 m/s enters a region of space where source charges have created an electric potential. What is the protons speed after it has moved through a potential difference of V = 100 V? f f i i K qV K qV + = + f i i f i K K qV qV K q V = +- =- 1 1 2 2 2 2 f i mv mv q V =- 2 5 2 1.44 10 m/s f i e v v V m =- = What is v f if the proton is replaced by an electron?...
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This note was uploaded on 06/07/2009 for the course PHYSICS 2212 taught by Professor Geist during the Fall '09 term at Georgia Perimeter.

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Phys2212_29.5+to+29.7 - Physics 2212 Electricity and...

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