DC / AC Devices Theory Questions - Section 7 - Basic Network Theorems

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Oct 10, 2013 (3 years and 9 months ago)

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DC / AC Devices Theory Questions
-

Section 7
-

Basic Network Theorems

Monday

October
17
, 2011
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T F 1.

When the
load resistance

equals the
source resistance
, maximum power is delivered
to the load from the source.

T F 2.

When maximum power is delivered to the load, load power dissipation equals

source resistance power dissipation.

T F 3.

Under maximum power transfer, the efficiency factor is 100%.

T F 4.

When the load resistance is greater than the source resistance, efficiency is less than
50%.

T F 5.

When the load resistance is less than the source resistance, efficiency is grea
ter than
50%.

T F 6.

At
maximum power transfer
, load voltage is 50% of the source voltage.

T F 7.

At maximum power transfer, load current is 50% of maximum source current.

T F 8.

An ideal voltage source has zero source resistance (
r
int
).

T F
9.

The
superposition theorem

is used to simplify circuit analysis where two or more
sources are present.

T F 10.

To disable other multiple voltage sources for purposes of calculations, consider them
open circuited.

T F 11.

The final results obtai
ned from the superposition theorem are determined by

algebraically adding the values obtained.

T F 12.

The direction of current flow and the polarity of the voltage drops are not

necessary using superposition theorems.

T F 13.

Thevenin's theorem

is

used to simplify complex networks to a simple voltage

source with its source resistance.

T F 14.

Solving a Thevenized circuit is as simple as solving a single resistor series circuit.

T F 15.

Thevenin's theorem deals with a simple parallel equival
ent circuit.

T F 16.

The Thevenized voltage is felt across the load resistor analyzed.

T F 17.

The Thevenized resistance is determined by shorting out the source voltage.

T F 18.

The Thevenized resistance is always in series with the load resis
tance.

T F 19.

Voltage divider analysis can be used to find load voltage in a Thevenized

equivalent circuit.

T F 20.

A current
-
related approach is used to
Nortonize a

complex circuit.

T F 21.

The Norton resistance is placed in series with the N
orton current source.

T F 22.

The Norton resistance can be found the same way the Thevenized resistance is

calculated.

T F 23.

The first step in Thevenizing a circuit is to remove the load.

T F 24.

The first step in Nortonizing a circuit is to
short out the load.

T F 25.

Norton's equivalent circuit is comprised of a constant current source with a

shunt (parallel) Norton resistance.

T F 26.

Thevenin's equivalent circuit is comprised of a voltage source with a series

Thevenin's resistance.

T F 27.

Norton's and Thevenin's theorems can be used on any network using any components.

T F 28.

Ohm's law cannot be used to calculate for voltage or current distributions

when using superposition, Thevenin or Norton equivalent circuits.

T F 29
.

Norton current is determined by assigning a value of zero ohm to the load resistance.

T F 30.

Norton resistance is found by looking back into the source from the open load
terminals (
with the current source opened
).

T F 31.

Thevenin's resistanc
e is found by looking back into the source from the open

load terminals (
with the voltage source shorted
).

T F 32.

Voltage sources must be shorted, current sources must be opened, and loads

must be removed to determine source resistance.

DC / AC Devices Theory Questions
-

Section 7
-

Basic Network Theorems

Monday

October
17
, 2011
-

presenterawful_3a5b1927
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23aa
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00fcfe145ebf.doc

S7
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33.

The theore
ms in this chapter deal with

A.

bilateral components.

B.

linear components.

C.

steady state conditions.

D.

All of the above.


34.

At maximum power transfer conditions,

A.

load voltage is 50% of maximum source voltage.

B.

load current is 50% of maximum sour
ce current.

C.

load resistance equals source resistance.

D.

All of the above.


35.

When load resistance is greater than source resistance

A.

efficiency is greater than 50%.

B.

efficiency is lower than 50%.

C.

efficiency equals 50%.

D.

None of the above.


3
6.

To use the superposition theorem,

A.

note the directions of current flow.

B.

note the polarity of the voltage drops.

C.

analyze one source at a time.

D.

All the above.


37.

Superposition can be used to analyze circuits containing

A.

single voltage sourc
es.

B.

single current sources.

C.

multiple current and/or voltage sources.

D.

None of the above.


38.

Norton’s theorem uses

A.

a voltage related approach.

B.

a current related approach.

C.

Both A and B.

D.

None of the above.


39.

To convert a Norton equiva
lent circuit to a Thevenin equivalent circuit,

A.

let the Norton resistance equal the Thevenin resistance.

B.

the product of Norton current and Norton resistance equals the Thevenin voltage.

C.

Both A and B.

D.

None of the above.


40.

To find the Norton pa
rameters from the Thevenin parameters,

A.

let the Thevenin resistance equal the Norton resistance.

B.

the Norton current is equal to the Thevenin voltage divided by the Thevenin resistance.

C.

Both A and B.

D.

None of the above.


DC / AC Devices Theory Questions
-

Section 7
-

Basic Network Theorems

Monday

October
17
, 2011
-

presenterawful_3a5b1927
-
23aa
-
41f4
-
b479
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00fcfe145ebf.doc

S7
Page
3

of
6

41.

The first steps to Nor
tonizing a circuit are:

A.

short R
L
, determine I
L
, make I
L

= I
N
.

B.

open R
L
, determine I
L
, make I
L

= I
N
.

C.

short R
L
, determine R
N
, make V
S
/R
N

= I
N
.

D.

open R
L
, determine V
L
, make V
L
/R
L

= I
N
.


42.

The first steps to Thevenizing a circuit are:

A.

short R
L
,
determine I
L
, make I
L

= I
th
.

B.

open R
L
, determine R
th
, make V
S
/R
th

= I
th
.

C.

open R
L
, determine V
L
, make V
L

= V
th
.

D.

open R
L
, determine I
L
, make R
L

x I
L

= V
th
.



Circuit values and parameters for
Figure 7
-
1:


V
s

= 12 V

R
1

=
R
3

= 470


R
2

= 910


R
L

= 1
k



Determine the following unknowns:


43.

R
th

= ______________


44.

V
th

= ______________



45.

Draw the Thevenized circuit.



46.

V
L

= ______________


47.

I
L

= ______________


Change the load resistance to 470


and recalculate t
he following:


48.

V
L

= ______________


49.

I
L

= ______________



Convert the
Thevenin

circuit of Question 43, 44 to a
Norton

equivalent circuit.


50.

I
N

= ______________


51.

R
N

= ______________


52.

Draw the Norton circuit below
.





DC / AC Devices Theory Questions
-

Section 7
-

Basic Network Theorems

Monday

October
17
, 2011
-

presenterawful_3a5b1927
-
23aa
-
41f4
-
b479
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00fcfe145ebf.doc

S7
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4

of
6

For the circuit of
Figure 7
-
1

on the previous page, calculate the load current and voltage
using the original circuit values of resistance and voltage. Use the basic rules for parallel and
series circuits only. Calculate for a load of 1 k


as well
as for a load of 470

. (This is for
practice using the longer method !)


53.

I
L 1 k



= _______



54.

V
L 1 k


= _______




55.

I
L

470


= _______



56.

V
L 470


= _______



57.

As far as the load voltage is concerned,
does it make any difference if you

Thevenize or Nortonize the circuit?


Answer: Yes or No.

Explain:




58.

As far as the load current is concerned, does it make any difference if you

Thevenized or Nortonized the circuit?


Answer: Yes or No.

Explain:



Circuit values and parameters
for
Figure 7
-
2:


V
s

= 24 V


R
1

= 3.3 k


R
2

= 6.8 k


R
3

= 7.5 k



R
4

= 5.1 k



R
L

= 1.2 k



Determine the following
unknowns:





59.

V
th

= ______________



60.

R
th

= ______________



61.

V
RL

= ______________



62.

I
L

= ______________


63.

Draw the equivalent circuit.



64.

Conventional current flows from point _______ through to point _______.


DC / AC Devices Theory Questions
-

Section 7
-

Basic Network Theorems

Monday

October
17
, 2011
-

presenterawful_3a5b1927
-
23aa
-
41f4
-
b479
-
00fcfe145ebf.doc

S7
Page
5

of
6

Referring again to
Figure 7
-
2

on the
previous page
, answer the following questions based on
the premise that th
e value of
V
s

is doubled to 48 V.


65.

V
th

would

A. double.


C. remain the same.

B. halve.


D. increase by fourfold.



66.

I
L

would

A. double.


C. remain the same.

B. halve.


D. decrease by one
-
fourth.



67.

The direction of current flow through R
L

would


A. remain the same.

B. reverse.



Circuit values and
parameters for
Figure 7
-
3:


V
s

= 100 V

I
s

= 200 mA


R
1

= 6.8 k


R
2

= 2.2 k


R
3

= 3.3 k


R
4

= 4.7 k



Determine the following
unknowns:



68.

R
T

for I
S

= ______________


69.

R
T

for V
S

= ______________



70.

I
R1

= ______________



71.

I
R2

= ______________



72.

I
R3

= ______________



73.

I
R4

= ______________



74.

V
R1

= ______________



75.

V
R2

= ____________
__



76.

V
R3

= ______________



77.

V
R4

= ______________



78.

V
A

= ______________



79.

V
B

= ______________


80.

V
BC

= ______________



81.

V
BA

= ______________


82.

Draw the equivalent current source circuit and the
voltage source circuit on a separate
piece of paper.
NOTE:

Refer to the figures you just drew. Verify your data with
Kirchhoff's voltage and current loops.



DC / AC Devices Theory Questions
-

Section 7
-

Basic Network Theorems

Monday

October
17
, 2011
-

presenterawful_3a5b1927
-
23aa
-
41f4
-
b479
-
00fcfe145ebf.doc

S7
Page
6

of
6

Answers for Questions 7a



1

T

2

T

3

F

4

F

5

F

6

T

7

T

8

T

9

T

10

F

11

T

12

F

13

T

14

F

15

F

16

F

17

T

18

T

19

T

20

T

21

F

22

T

23

T

24

T

25

T

26

T

27

F

28

F

29

T

30

T

31

T

32

T

33

D

34

D

35

A

36

D

37

C

38

B

39

C

40

C

41

A

42

C

43

779.93


44

7.913 V


45

Draw a voltage source of 7.91 V in series with a 780 ohm
source resistance.

46

4.446 V

47

4.446 mA

48

2.9755 V

49

6.331 mA

50

10.146 mA

51

779.93




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