2

Circuit Elements

a

Assessment Problems

AP 2.1

[a] Note that the current

i

b

is in the same circuit branch as the 8 A current

source; however,

i

b

is defined in the opposite direction of the current

source. Therefore,

i

b

=

-

8A

Next, note that the dependent voltage source and the independent

voltage source are in parallel with the same polarity. Therefore, their

voltages are equal, and

v

g

=

i

b

4

=

-

8

4

=

-

2V

[b] To find the power associated with the 8 A source, we need to find the

voltage drop across the source,

v

i

. Note that the two independent sources

are in parallel, and that the voltages

v

g

and

v

1

have the same polarities,

so these voltages are equal:

v

i

=

v

g

=

-

2V

Using the passive sign convention,

p

s

= (8 A)(

v

i

) = (8 A)(

-

2 V) =

-

16 W

Thus the current source generated 16 W of power.

2–1

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All rights reserved. This publication is protected by Copyright and written permission should be

obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic,

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2–2

CHAPTER 2. Circuit Elements

AP 2.2

[a] Note from the circuit that

v

x

=

-

25 V. To find

α

note that the two

current sources are in the same branch of the circuit but their currents

flow in opposite directions. Therefore

αv

x

=

-

15 A

Solve the above equation for

α

and substitute for

v

x

,

α

=

-

15 A

v

x

=

-

15 A

-

25 V

=0

.

6 A/V

[b] To find the power associated with the voltage source we need to know the

current,

i

v

. Note that this current is in the same branch of the circuit as

the dependent current source and these two currents flow in the same

direction. Therefore, the current

i

v

is the same as the current of the

dependent source:

i

v

=

αv

x

= (0

.

6)(

-

25) =

-

15 A

Using the passive sign convention,

p

s

=

-

(

i

v

)(25 V) =

-

(

-

15 A)(25 V) = 375 W

.

Thus the voltage source dissipates 375 W.

AP 2.3

[a] The resistor and the voltage source are in parallel and the resistor voltage

and the voltage source have the same polarities. Therefore these two

voltages are the same:

v

R

=

v

g

= 1 kV

© 2010 Pearson Education, Inc., Upper Saddle River, NJ.

All rights reserved. This publication is protected by Copyright and written permission should be

obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic,

mechanical, photocopying, recording, or likewise. For information

regarding permission(s), write to: Rights and Permissions Department,

Pearson Education, Inc., Upper Saddle River, NJ 07458.