L11_Viet_Electric Potential_Equipotential_Surfaces

L11_Viet_Electric Potential_Equipotential_Surfaces -...

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Physics 122 Electricity and Magnetism Lecture 11 Electric Potential, Equipotential Surfaces

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05/12/09 Physics 122 - Lecture 11 2 The Electric Potential 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. Example: A cell battery has a potential of 1.5 V between its terminals.
05/12/09 Physics 122 - 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, we’ll 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

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05/12/09 Physics 122 - 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 proton’s speed after it has moved through a potential difference of V = 100 V? f
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This note was uploaded on 04/25/2009 for the course ECE PHYS122 taught by Professor Viet during the Spring '09 term at 東京大学.

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L11_Viet_Electric Potential_Equipotential_Surfaces -...

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