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chp30_3 - from infinity and placing them on the capacitor...

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PHY2061 R. D. Field Department of Physics chp30_3.doc University of Florida Energy Density of the Electric Field Energy Density u: Electric field lines contain energy! The amount of energy per unit volume is u = e 0 E 2 /2 , where E is the magnitude of the electric field. The energy density has units of Joules/m 3 . Total Stored Energy U: The total energy strored in the electric field lines in an infinitessimal volume dV is dU = u dV and U udV Volume = If u is constant throughout the volume, V, then U = u V. Example: Parallel Plate Capacitor Think of the work done in bringing in the charges
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Unformatted text preview: from infinity and placing them on the capacitor as the work necessary to produce the electric field lines and that the energy is strored in the electric field! From before we know that C = A ε /d so that the stored energy in the capacitor is U = Q 2 /(2C) = Q 2 d/(2A ε ) . The energy stored in the electric field is U = uV = e E 2 V/2 with E = σ /e 0 = Q/(e A) and V = Ad , thus U=Q 2 d/(2A ε ), which is the same as the energy stored in the capacitor! Volume E +Q-Q d Area A E-field...
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