lecture2

# lecture2 - Physics 2102 Jonathan Dowling Physics 2102...

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November 18, 2011 Physics 2102 Physics 2102 Lecture 2 Lecture 2 Electric Fields Electric Fields Charles-Augustin de Coulomb (1736-1806) Physics 2102 Jonathan Dowling Version: 1/17/07

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What are we going to learn? What are we going to learn? A road map A road map Electric charge Electric force on other electric charges Electric field , and electric potential Moving electric charges : current Electronic circuit components: batteries, resistors, capacitors Electric currents Magnetic field Magnetic force on moving charges Time-varying magnetic field Electric Field More circuit components: inductors. Electromagnetic waves light waves Geometrical Optics (light rays). Physical optics (light waves)
2 q - 12 F 1 q + 21 F 12 r Coulomb’s law Coulomb’s law 2 12 2 1 12 | | | | | | r q q k F = 2 2 12 0 0 10 85 . 8 with 4 1 m N C k - × = = ε πε 2 2 9 10 99 . 8 C m N × k = For charges in a VACUUM Often, we write k as:

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Electric Fields Electric Fields Electric field E at some point in space is defined as the force experienced by an imaginary point charge of +1 C, divided by 1 C. Note that E is a VECTOR . Since E is the force per unit charge , it is measured in units of N/C. We measure the electric field using very small “test charges”, and dividing the measured force by the magnitude of the charge. 2 | | | | R q k E = +1 C R E q Electric field of a point charge
Superposition Superposition Question : How do we figure out the field due to several point charges? Answer : consider one charge at a time, calculate the field (a vector!) produced by each charge, and then add all the vectors! (“superposition”) Useful to look out for SYMMETRY to simplify calculations!

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4 charges are placed at the corners of a square as shown. What is the direction of the
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## This note was uploaded on 11/18/2011 for the course PHYSICS 2102 taught by Professor Dowling during the Fall '10 term at LSU.

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lecture2 - Physics 2102 Jonathan Dowling Physics 2102...

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