# lecture3 - Ele ctric Fie II lds Ele ctric Fie lds Ele ctric...

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Electric Fields II

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Electric Fields Electric fields are produced by point charges and continuous charge distributions Definition: F qE = ur r . E r q F r is force exerted on charge by an external field Note: q produces a field but it is not external
E = ? + + + + + + + + + + + Source + Continuous Charge Distributions Continuous Charge Distributions Cut source into small (“infinitesimal”) charges dq Each produces 2 ( ) ˆ e dq dE k r = r uur dE r r dq 2 e dq dE k r = or

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Steps: Draw a coordinate system on the diagram Choose an integration variable (e.g., x ) Draw an infinitesimal element dx Write r and any other variables in terms of x dq in terms of dx Put limits on the integral Do the integral or look it up in tables.
Example Example : Uniformly-Charged Thin Rod : Uniformly-Charged Thin Rod (length L , total charge Q ) L d ? = E r Charge/Length = “Linear Charge Density” constant = Q/L 2 rod rod e dq E dE k r = = ur uur + + + + + + + + + λ

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Solution:
In 2D problems, integrate components separately

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## This note was uploaded on 01/23/2011 for the course ENG 1D04 taught by Professor Done during the Spring '08 term at McMaster University.

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lecture3 - Ele ctric Fie II lds Ele ctric Fie lds Ele ctric...

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