reviewch21-24

# reviewch21-24 - Fields Grass Seeds Know how to read Field...

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4 P13 - Fields Grass Seeds Know how to read Field Lines Know how to draw • Field line density tells you field strength • Lines have tension (want to be straight) • Lines are repulsive (want to be far from other lines) • Lines begin and end on sources (charges) or

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6 P13 - E Field and Potential: Creating A point charge q creates a field and potential around it: 2 ˆ ; ee qq kV k rr == Er G Use superposition for systems of charges ; B BA A VVVV d =−∇ =− EE s GG G They are related:
7 P13 - E Field and Potential: Creating 2 ˆ ; ee qq kV k rr == Er G Discrete set of point charges: Add up from each point charge 2 ˆ ; dq dq dk d V k G Continuous charge distribution : Break charged object into small pieces, dq , and integrate

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8 P13 - Continuous Sources: Charge Density Charge Densities: Q A σ= Q V ρ= L Q = λ dV dQ ρ = dL dQ = dA dQ σ = Don’t forget your geometry: 2 dA rdr π = 2 cyl dV rldr = 2 4 sphere dV r dr = dL dx = dL Rd θ =
9 P13 - E Field and Potential: Creating 2 ˆ ; ee qq kV k rr == Er G Discrete set of point charges: Add up from each point charge 2 ˆ ; dq dq dk d V k G Continuous charge distribution : Break charged object into small pieces, dq , and integrate Symmetric charged object: 0 S ; in q dV ε ⋅= ∆ −⋅ ∫∫ EA E s G GG d Use Gauss’ law to get E everywhere, then integrate to get V G w

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10 P13 - 0 S in q d ε ⋅= ∫∫ EA G w Gauss’s Law: Gaussian Pillbox Spherical Symmetry Planar Symmetry Cylindrical Symmetry
11 P13 - E Field and Potential: Effects q = FE G G If you put a charged particle, q , in a field: To move a charged particle, q , in a field: WU q V = ∆=∆

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13 P13 - Conductors in Equilibrium Conductors are equipotential objects: 1) E = 0 inside 2) Net charge inside is 0 3) E perpendicular to surface 4) Excess charge on surface 5) Shielding – inside doesn’t “talk” to outside 0 ε σ = E
P13 - Capacitors To calculate: 1) Put on arbitrary ±Q 2) Calculate E 3) Calculate V Q C V = Capacitance In Series & Parallel ,parallel 1 2 eq CC C = + series 1 2 11 1 eq, C =+ Energy 2 33 2 o E E udr dr ε == ∫∫∫ 2 2 2 1 2 1 2 V C V Q C Q U = = =

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17 P13 - Dielectrics Dielectrics locally weaken the electric field 0 ;1 E E κ =≥ 0 CC = Inserted into a capacitor: Q C V = Hooked to a battery? Q increases Not hooked up? V decreases
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## This note was uploaded on 10/25/2010 for the course PHYS 260 taught by Professor Hkmiet during the Spring '08 term at George Mason.

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reviewch21-24 - Fields Grass Seeds Know how to read Field...

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