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Unformatted text preview: 5/16/2011 1 PHY 2049: Physics II s We begin with a live clicker on Wednesday. s Wileyplus homework should be fully operational. s Tea and Cookies: We meet on Tuesdays at 5:00PM for tea and cookies in room 2165. quiz s The electric field at a distance of 1 m from an isolated point particle with a charge of 2 nC is: s A. 1.8N/C B. 180N/C C. 18N/C D. 1800N/C E. none of these Quiz 2 s An isolated charged point particle produces an electric field with magnitude E at a point 2m away from the charge. A point at which the field magnitude is 4E is: s A. 1m away from the particle s B. 0.5m away from the particle s C. 2m away from the particle s D. 4m away from the particle s E. 8m away from the particle PHY 2049: Physics II Last week s Coulomb’s law, Electric Field and Gauss’ theorem Today s Electric Potential Energy and Electric Potentials s Numerous cases Potential Energy and Potential s Force => work => change in K=> change in Potential energy s Δ U = U f – U i = W =  Δ K s Work done is path independent. K+U = constant. U = k q 1 q 2 /r : interaction energy of two charges. Sign matters PHY 2049: Physics II s Electric Potential s V = U/q = W/q s Units of Joules/coulomb = volt s 1 eV = e x 1V = 1.6 x 1019 J s Also s V = kq/r s V f –V i = ∫E.ds s In case of multiple charges, add as a number 5/16/2011 2 PHY 2049: Physics II s V fV i = ∫ k q/r 2 dr s Choose V i = V (∞)=0 s V(r) = kq/r s V = kpcosθ/r 2 s E =  ∂ V/ ∂ s =  s Uniformly charged disk s V = ?? A B C p r Consider the electric dipole shown in the figure We will determine the electric potential created at point P by the two charges of the dipole using superpos V Example : Potential due to an electric dipole ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ition. Point P is at a distance from the center O of the dipole. Line OP makes an angle with the dipole axis 1 4 4 We assume that where is o o r r r q q q V V V r r r r r d d θ πε πε + + + +  = + = = & ( ) ( ) 2 ( ) ( ) 2 2 the charge separation From triangle ABC we have: cos cos 1 cos Also: 4 4 where the electric dipole moment o o r r d q d p r r r V r r p qd θ θ θ πε πε + + ≈ ≈ → ≈ = = = (24  6) 2 1 cos 4 o p V r θ πε = dq O A Potential created by a line of charge of length L and uniform linear charge density λ at point P. Consider the charge element at point A, a distance from O. From triangle OAP we dq dx x λ = Example : ( 29 ( 29 ( 29 2 2 2 2 2 2 2 2 2 2 2 2 2 2 have: Here is the distance OP The potential created by at P is: 1 1 4 4 4 ln 4 l l n ln 4 n o o L o L o o r d x d dV dq dq dx dV r d x dx V d x V x d x V L...
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This note was uploaded on 12/05/2011 for the course PHY 2049 taught by Professor Any during the Spring '08 term at University of Florida.
 Spring '08
 Any
 Physics, Work

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