Elec. Potential - PHY 2049C General Physics B Fields,...

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PHY 2049C – General Physics B Fields, Circuits, Waves, Light Today: 1) Gauss' Law PHY 2049C – General Physics B Fields, Circuits, Waves, Light Today: 1) Electric potential
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Summary: Force, Field and Flux Charge: Matter contains + and charges [C] Force: [N] Field: [N/C] Flux: [Nm 2 /C] 12 2,1 2,1 2 , Coulomb Force qQ Fm a , F = k r r = GG G () 2,1 2 21 1 2 1 /C o u l o m b F i e l d F Q EF q , E r = = k r , qr = G G inside inside 0 4 Gauss' Law net N Q Φ Ed A = π kQ = ε =
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Out with vectors In with scalars Mechanics problems can sometimes be solved using forces or using energy Force is a vector and energy is a scalar, so energy is usually easier One exception is friction. Since friction does not conserve mechanical (kinetic + potential) energy, most problems involving friction forces are hard to solve using energy.
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Reminder: Potential Energy Lift a brick of mass m from y 1 to y 2 What is the work done on the brick? Work done by hand W ext is “absorbed” into the system W ext can be retrieved: take the hand away and the brick will retrieve it as kinetic energy: The work has been stored in lifting the brick's position : This form of energy is Potential Energy U = mgh cos0 ext ext WF d m g h m g h == = D 22 11 2( 2 ) vg h K m vm g h m g h =⇒ = = =
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Mechanical Potential Energy - Electric Potential Energy Electric P.E. (U) is just another form of P.E. and can be converted into kinetic or any form of energy. The force always points towards the lower U () ab ba b a W= F o r c e P a t h UU m g hh × −= F = m g High PE Low PE a b High PE Low PE F = q E b a WF o r c e P a
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This note was uploaded on 06/29/2010 for the course PHY2049C PHY2049C taught by Professor Duke during the Summer '10 term at FSU.

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Elec. Potential - PHY 2049C General Physics B Fields,...

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