q1 - a (15 points) exam2-solution.pdf · q1 - a (15 points) write the mesh equations for i1, i2,...
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Q1 - a (15 points)
Write the mesh equations for i1, i2, i3, and i4 in the matrix form
(Note: Don’t solve for the mesh currents i1, i2, i3, and i4)
Solution
From the super-mesh
2i1 + 8(i1-i4) + 3(i3-i4) + 4(i3-i2) = 0
10i1 - 4i2 + 7i3 - 11i4 = 0 ----(1)
i1 – i3 = 2 ----- (2)
Mesh-2
-20 + 5i2 + 4(i2-i3) = 0
9i2 + -4i3 = 20 ----(3)
Mesh-4
-10 + 3(i4-i3) + 8(i4 – i1) = 0
-8i1 - 3i3 + 11i4 = 10 ----(4)
Q1 – b (15points)
Given that
i3 = 0.5 A i4 = -2 A
a) Solve for i1 and i2
b) Calculate the branch currents (ia and ib) c) Calculate the voltages (Vc and Vd)
d) Calculate the power delivered by the 3 A current source.
Solution
a)
i1 = 3 A
i2= -2 A
b)
ia= i3-i4 = 0.5 +2 = 2.5 A
ib= id+2 = (i2-i3)+2 = (-2-0.5)+2 = -0.5 A
c)
Vc = -10 ( i2 )= -10 ( -2) = 20 V
Vd= 5 (i2 – i3) = 5(-2-0.5) = -12.5 V
d)
V15Ω = 15(i1-i3) = 15(3-0.5) = 15(2.5) = 37.5 V )
P3A = -(3)(37.5) = - 112.5 W
Q2 (20)
+ −
2 xi
+−
2 Ω
3 Ωxi
10 V
a
b
For the circuit shown above , find the followings :
(a) The open circuit voltage between terminals a and b ?
(b) The short circuit current through the terminals a and b ?
(c) The Thevenin equivalent resistant between terminals a and b ?
(d) The load resistant RL between terminals a and b that will absorb the maximum power ? (e) The maximum power absorbed by the load resistant RL in part (d) ?
Solution
+ −
2 xi
+−
2 Ω
3 Ωxi
10 V
a
b
OCV
+
− OC OC
10 5 0 2
3 2 V 0 V 2 V
x x
x x
i i A
i i
− + = ⇒ =
− + + = ⇒ =
KVL on loop 1
KVL on loop 2
0 A( ) a (6)
+ −
2 xi
+−
2 Ω
3 Ωxi
10 V
a
b
3V 3 2 0 x x xi i iΩ = = ⇒ =
scI3V Ω
+
− sc10
I I 5 2
A= = =I
( ) b (6)
OC
SC
TH
(c)
V 2R
I 5= = Ω
L TH
(d)
2R R
5= = Ω
2oc
maxTH
(d)
V 4 5P = 2.5 W
4R 4(2 /5) 2= = =
Q3 (25)
Part I For the RC circuit shown below , the voltage across the capacitor and the current through the capacitor are
RC (t)
v+
−
(t)i
10tv(t) = 35e V for t > 0
−
10ti(t) = 7e mA for t > 0
−
Circle the correct answer :
(a) The value of the resistor R is
1 1(i) 7 k (ii) 200 k (iii) 35 k (iv) 5 k (v) k (vi) k5 200
Ω Ω Ω Ω Ω Ω
(a) The value of the capacitor C is
(i) 2000 µF (ii) 250 µF (iii) 200 µF (iv) 20 µF (v) 10 µF (vi) 5 µF
Part II The equivalent capacitance between terminals a and b in the
circuit shown below is 8 µF .
a
b
(c) The value of the capacitor C is (Circle the correct answer ) (i) 6 µF (ii) 5 µF (iii) 8 µF (iv) 2 µF (v) 10 µF (vi) 4 µF
Part III The voltage v(t) across a 2 mF capacitor is shown below
16
0 1 2 3 4t
v(t)
(d) Plot current i(t) through the capacitor showing all significant values ?
i(t) mA
t0 1 2
3 4
5
32
32