ENGR 12
Assignment 14 Revised
Due: next wed
Part I. Drills -- 1 point each
1) Use Mesh Current to solve for phasor voltage Vo
2) Use Mesh Current to solve for phasor current I
3) Find the coupling coefficient k for problems 1 and 2 above. Assume that w = 2 radians/sec and remember
that ZL = jwL.
4) Find the energy in the circuit in problem 1 at t = 1 second assuming w = 2 radians/sec.
5) Find the input impedance seen by the voltage source for the circuit in problem 1.
Part II. Assisted Problem Solving – 2 pts
6) a) With a source voltage Vs = 25<0 kV, solve for phasor
V2 and I2 in the ideal transformer. b) how much power
is being delivered to the 4-j14.4 load ? c) What turn
ratio would give the max power to the load? d) and
what would the max power be?
7) Find the Thevenin equivalent at terminals c-d
Plan: Part a)
1) Recall that ZL' = V1/I1 = ZL/n2
2) Zin = ZL' + 1.5k + j6k
3) I1 = Vs/Zin
4) I2 can be found by transformer relation
5) V2 can be found by I2*ZL
Part b)
6) Power = V2(I2*)
Part c)
7) Zth for source = 1.5 + j6. Set |ZL/n2|= |Zth|
and solve for n (remember n = N2/N1)
Part d)
8) re-solve for V2, I2 and recompute the new load
power
PLAN
1) Find Voc at c-d using mesh analysis realizing that
I2 = 0 due to the open circuit.
2) Find Isc at c-d again using mesh analysis
3) Find Zth = Voc/Isc
4) Find Vth = Voc
Part III. Unassisted Problem Solving – 3 points
8) The coupling coefficient k is adjusted until the input impedance Zab is resistive. Find k and Zab when w = 4000 R/sec.
Recall for a linear transformer
2
2
Zin 
V
M
 R1  jL1 
I1
R2  jL2  Z L