EE 250 Winter 2010
University of Alberta
SOLUTIONS TO
HOMEWORK 2
Instructor : Karthik Shankar
(The ten problems are arranged in order of increasing difficulty.
Make sure your
answers show the work in solving the problem.
If the final answer is wrong, partial
credit will be provided if the work is shown to have made progress towards the
solution.
Do not expect any credit if the T.A. cannot logically follow what you have
put on your submitted homework.
Make sure you include units with each answer.)
1.
A coil has a resistance of 20
Ω
and an inductance of 4 H.
It is connected to a 50 V
DC supply; a) Find the time constant of the circuit
b) Find the value of the current
flowing after 0.1 s and c) Find the time required for the current to grow to 1.5 A.
Solution
a) Time constant of the circuit (
τ
c
) =L/R =0.2 s.
b)
0.5
()
(1
)
(0.1 )
2.5(1
)
0.983
c
t
s
V
it
e
R
is
e
τ
−
−
=−
=−=
A
c)
0.2
0.2
( )
2.5(1
) 1.5
2.5 1.5
0.4
2.5
0.2ln(0.4)
0.18
x
x
ix
e
e
x
s
−
−
=
−
==
=
2.
A circuit consists of an uncharged capacitor connected in series with a 50 k
Ω
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 Spring '10
 Shankar
 RC circuit, RL circuit, K1, RC, ln vL

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