EECS
314
Winter 2008
Homework set 5
Student’s name ___________________________
Discussion section # _______
(Last, First, write legibly, use ink)
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Instructor is
not responsible
for grading and entering scores for HW papers lacking clear
information in the required fields above
Scores for the HW set:
Problem
1
2
3
4
5
6
7
Total
Score
Problem 1 Energy stored in inductors and capacitors at DC
Part
1
2
3
Total
The Big Picture
1.
Inductors store energy in the form of magnetic field. The energy W stored in the
inductor equals
2
2
1
I
L
W
⋅
⋅
=
where L is the inductance and I is current through the
inductor. Units: if L is in henrys and I is in amps, then W is in joules.
2.
Inductors act as short circuits under DC steady-state conditions. There is no
voltage drop across the inductor under DC steady-state conditions.
3.
Capacitors store energy in the form of electric field. The energy W stored in the
capacitor equals
W
=
1
2
⋅
C
⋅
V
2
where C is the capacitance and V is the voltage
across the capacitor. Units: if C is in farads and V is in volts, then W is in joules.
4.
Capacitors act as open circuits under DC steady-state conditions. They do not
conduct DC current, and the voltage across the capacitor is determined by the voltage
across the circuit elements (sources, resistors, etc.), with which this capacitor is in
parallel.
5.
In order to calculate the energy stored in the inductors and capacitors under DC
steady-state conditions, use the following strategy:
a.
Redraw the circuit replacing each capacitor with an open switch and each
inductor with the closed switch.
b.
In this redrawn circuit, determine the current through each inductor (each
closed “switch”) and the voltage across each capacitor (each open
“switch”).
6.
Then apply the formulas for energy listed above. Be careful with the units of
measure!
© 2008 Alexander Ganago
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