SUNY Geneseo, Department of Physics and Astronomy Physics 125: Analytical Physics IITypes of Gauss’ Law Problems There are a limited number of Gauss’ Law problems, and certain types of equations that will always com up in each type. Notation: Below, I’ll always use rfor the radius of the Gaussian surface, and use afor the radius of physical charged objects. It is rarely the case that you want rand ato be the same. Problem Type Charge densities likely to be involved Conductor with Cavity Alwaysuse a Gaussian surface that passes through “the meat” of the conductor (shape is unimportant), so that 0encsurroundedinner surface0qQQε=Φ= =+Likelyto want to use charge conservation on the conductor: conductorouter surfaceinner surfaceQQQ=+Q, σSpherical Symmetry Alwaysuse Gaussian surface (sphere with radius r), so that ()200enc4Erqεπ=Likelyto want to use some combination of the following to get qenc 24qaσπ=343ρπ⎛⎞=⎜⎟⎝⎠Q, , ρ Cylindrical Symmetry(infinitely long)
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This note was uploaded on 05/22/2008 for the course PHYS 125 taught by Professor Iyer during the Spring '08 term at SUNY Geneseo.