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Sample problem
Topic: Power and energy
Problem statement
The voltage and current at the terminals of the circuit element in following figure are zero
for t<0.
For t>0 they are
1000
1000
75 75
50
t
t
ve
V
ie
m
A
−
−
=−
=
(a) Find the maximum value of the power delivered to the circuit.
(b) Find the total energy delivered to the element.
Problem solution
(a) The first thing is to find out the expression of power
1000
1000
3
1000
2000
(75 75
)(50
10 )
(3.75
3.75
)
tt
t
t
Pv
i
e
e
e
e
W
−−
−
−
−
== −
×
=
−
Recall that what is learned in calculus, or that the maximum value happens at the zero
point of the derivative function
1000
2000
3750
7500
0
dP
ee
dt
+
=
By solving the above equation, the maximum point is obtained
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This note was uploaded on 10/30/2011 for the course EE 215 taught by Professor Unknown during the Spring '05 term at University of Washington.
 Spring '05
 Unknown
 Electrical Engineering, Volt

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