# HW4answers - t ∆ t = C ∆ v / i =...

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HW 4 answers P3.1 – Describe the construction of capacitors. Answer – Capacitors consist of two parallel thin plate conductors separated by a thin layer of insulating material. P3.3 – If the voltage across a capacitor is constant, what is the value of the current? Explain why. Answer – Because i = C dv/dt for a capacitor, the current is zero if the voltage is constant. Thus we say that capacitances act as open circuits for constant DC voltages. P3.4 – The voltage across a 100 uF (microfarad) capacitor is 200 V. What is the magnitude of the net charge stored on each plate? What is the total net charge stored on both plates? Answer – The net charge on each plate is Q=CV=(100e-6)x200=.02 C. One plate has a net positive charge and the other has a net negative charge so the net charge for both plates is zero. Answer: i = C dv/dt = C ∆ v /∆
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Unformatted text preview: t ∆ t = C ∆ v / i = (2000E-6)(100)/(100E-6) = 2000 sec P3.36 Describe the construction of inductors. Answer – Inductors consist of coils of wire wound on coil forms such as toroids. P3.37 – If the current through an inductor is decreasing in magnitude, is the energy flowing into or out of the inductor? Answer – Because the energy stored in an inductor is W= ½Li 2 , the energy stored in the inductor decreases when the current magnitude decreases. Therefore, the energy is flowing out of the inductor. P3.38 – If the current through an inductor is constant, what is the value of the voltage across the inductor? Explain why. Answer – Because v L ( t ) = L di L ( t )/ dt , the voltage is zero when the current is constant. Thus we say that inductors act as short circuits for steady DC currents....
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## This note was uploaded on 09/01/2010 for the course EE 331 taught by Professor Preston during the Spring '06 term at University of Texas at Austin.

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