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**Unformatted text preview: **Mid-Term Examination of Electromagnetics (H) l) (20%) In system shown in FigPl, the switch S is closed at [=0 The line voltage variations
with time at :=0 and z: 6’ for the ﬁrst Sus are observed to be as shown in Fig.PI( b) and (c).
respectively. Find the values of V0, Rg, RL, and T. 9% ma. v
f .=.. mo}
R ‘41.) ‘ _
l 1.. = (min :- h
f—‘l'fl-ﬂ w
’r . p ”a... ‘_sl _mﬁ_._ ‘
; = u [:5 n (I 3 .3 h H
.1) _ th‘l _
FigPi _ “l
. . . . .Xr. ﬁrm-F— - ch)
2) (20%) In the system shown m FigPZ, the swrtch S [S F H A LCa—i
closed at (=0, with the voltage across the capacitor 22% 7 v C?”
equal to zero. Find and plot the voltage (a) I/‘(t’L t) y _5_ 2.2:;
for {<22T; and (b) V (E, t) for V137". D ﬂn———_—_—4_:%
get] 1;"
3) (20%) In the system shown in Fig.P3, a line of Flo P”
characteristic impedance T: Q and charged to 10V is J
connected at IZO to another line of characteristic PM '. U:::_~———-_-3
impedance 509 and charged to 5V. The one-way ‘ l H 2 1
rev .1- I L 4,: 30:2 <v
travel time Tis equal to lus for both lines. Find (a) g ’= ' m T= i m .- —— —' — “vintage—distribution at Eff LE; (6') current disfnbmfoii
at t=2us; (c) voltage waveform at the left open end
2: 0) up to ﬁns; and (d) the period of the waveform. Reference
Perm Lind 4) (20%) A slotted coaxial line of characteristic , l
impedance 75.0 was used to measure an unknown my“
(a) load impedance as shown in Fig.P4. First, the _ 20m_ﬂ . receiving end of the line was short-circuited. The I voltage minima were found to be 20cm apart. One (b) [\m—T of the minima was marked as the reference point. 9 ‘5cm—‘i ;
Next. the unknown impedance was connected to Trig P 4 the receiving end of the line. The SWR was found to be 3.0 and a voltage minimum was found to be .1 0.115A—-———-—~~+ 15cm from the reference point toward the Menace. { my“?
(a) Find the value of the unknown load impedance. mmnmL l 7 ﬂ_. 4., 7 mu i2 9.
(b) The load can be matched to the coaxial line by WW (1; I ‘
inserting a section of transmission line at E. Find ._ LEJ
the characteristic impedance and length of the “I d J ‘”
inserted line. :13 P ‘2" 5) (20%) In the system in FigPS. find (a) the value ofthe load impedance ZR that enables
maximum power transfer from the generator to the load and (b) the power transferred to the load
for the value found in (a). 6) ‘ftﬁisider driver - load circuit shown in Fig.P6_ Two inverters are connected by a transmission
line of characteristic impedance 20 and delay time To The transistors are assumed ideal, i.e., Q] is
ON and Q2 is OFF when Viv is low, Qi is OFF and Q2 is ON when Vm is high, and the input
impedance to the inverter (or the impedance seen to the gate) is assumed to be open circuit. Let
the transmission line be initially in the low state, i.e., Vi = V3 = 0‘ A periodic pulse in incident to
the driver with the voltage V»; negative (i.e., l7“ : V00 e Vm) shown in Fig.P6(b)_ The period is
much larger than T, say lOT. Please plot (a) the voltage at the driver end Vim, (b) the voltage at the receiver end Vgﬁ), (c) the total current ﬂowing through the resister of Zn, and (d) the power
dissipation in the system Pm. Ql i: 2 i0 Remark: The examination takes from 10:10 — l2:00. You need only ﬁnish ﬁve of the six
problems. If you have done all of the six, the one with the least score will not be accounted. ...

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- Fall '08
- Electromagnet, Volt