# lecture3 - Electric Fields II Electric field produced by...

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Electric Fields II •Electric field produced by point charges •Continuous charge distributions Text sections 23.4, 23.5 Practice: Chapter 23 , problems 23, 25, 27, 33 Several point charges: r E ˆ 2 r q k e = Point charge q: i i i i e r q k r E ˆ 2 = E is the vector sum of the fields produced by the individual charges.

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Example: Dipole Example: Dipole Derive an expression for at point B. E r y aa x B : (0,y) A : (x,0) -q +q ) i ˆ ( 2 3 = r qa k e E 2 1 2 2 ) ( a y r + = where Answer: A note on “style”: the final result is given in terms of the variables in the original problem ( a, q, and y ). Note… 3 1 r E r (dipole) For fun: find E at point A, and show that it is approximately proportional to x 3 , at large distance x .
E = ? + + + + + + + + + + + Source + Continuous Charge Distributions Continuous Charge Distributions •Cut source into small (“infinitesimal”) charges dq •Each produces r dE ˆ ) ( 2 r dq k e = Total, r E ˆ source 2 = r dq k e dE r r dq Example Example : Uniformly : -Charged Thin Rod Charged Thin Rod (length L , charge Q ) L b ? = E r Charge/Length =

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## This note was uploaded on 12/03/2009 for the course CHEMISTRY 1E03 taught by Professor Britz during the Spring '09 term at McMaster University.

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lecture3 - Electric Fields II Electric field produced by...

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