Download 35Final Review I

5/19/03 Minute Paper
• If a piezo-electric motor can expand and contract with
voltage, can it also produce a voltage when it is
expanded or contracted?
• Is the review going to go through each chapter or are we
just going to ask questions and you answer them? Is
there going to be any material on the final that will test us
on how to use tools that we used in the lab (oscilliscope,
multimeter, etc.)
• How is current generated by the rotor blades while flight?
This happens in a greater magnitude on humid day and
when they fly over the ocean, why?
Topic 1: DC & AC Circuit Analyses
• KCL, KVL: mesh or nodal analyses. Work for both dc
and ac circuit. In ac circuits, use impedance and phasor.
• Thévenin and Norton equivalent circuit.
• Transient circuits: charging and discharging Capacitors
• AC power: average and instantaneous (complex) power,
power factor, power factor correction.
• Three Phase power: structure and advantages
Mesh Analysis
Example: 2 meshes
Step 1: Assignment of mesh currents (clockwise)
(mesh is a loop that does not contain other loop).
Step 2: Apply KVL to each mesh
•
•
•
•
The so-called self-resistance is the effective resistance of the
resistors in series within a mesh. The mutual resistance is the
resistance that the mesh has in common with the neighboring
mesh.
To write the mesh equation in standard form, evaluate the
self-resistance, then multiply by the mesh current. This will
have units of voltage.
From that, subtract the product of the mutual resistance and
the current from the neighboring mesh for each such
neighbor.
Equate the result above to the driving voltage, taken to be
positive if its polarity tends to push current in the same
direction as the assigned mesh current.
Mesh 1
(R1+R2)I1
Mesh 2
- R2I1
Step 3: Solve currents
- R2I2
(R2+R3)I2
= e1 - e2
= e2 – e3
Sample circuit: 3 meshes
Mesh 1:
Mesh 2:
Mesh 3:
Mesh Analysis with Current Source
i2   I S
( R1  R2 )i1  R2i2  VS
i1
i2
i1 
VS  R2i2 VS  R2 I s

R1  R2
R1  R2
Example 1
b.In the circuit at right, find the value of Is that will reduce
the voltage across the 4 ohm resistor to zero.
What if the 2 ohm and 6 ohm are interchanged?
12i1  4i2  10
i1  10 / 8  1.25 A
i2  I S
I S  1.25 A
i1  i2  0
12i1  4i2  10
i2  I S
i1  i2  0
Example 2:
Ex.2: Which of the two circuits has the larger terminal voltage: A or B?
Which of the two circuits has the larger current through the 9 V battery: A or B?
Circuit A
Circuit B
Terminal voltage
1.64 V
1.10 V
Current through 9V battery
0.41 A
-0.56 A
18.6i1  0.6i2  9  1.5  7.5
18.6i1  0.6i2  9  1.5  10.5
 0.6i1  10.6i2  1.5V
 0.6i1  10.6i2  1.5V
terminal voltage :
9  0.4118  1.64V
terminal voltage :
0.56 18  9  1.10V
Thévenin and Norton Equivalent Circuits
Thévenin Equivalent Circuit
Norton Equivalent Circuit
How do we calculate RT, VT, iN, RN?
Calculation of RT and RN
• RT=RN, same calculation
• Setting all sources to be zero (“killing” the sources)
– Voltage source: short
– Current source: open
• Calculate equivalent resistance seen by the load.
Calculation of VT
Remove the load and calculate the open circuit voltage
Calculation of IN
short the load and calculate the short circuit voltage
R1  R2 i1  R2iSC  vS
 R2i1  R1  R2 iSC  0
vS  v v
v


R1
R2 R3
iN  iSC
vS R2

R1R3  R2 R3  R1R2