978-0128012420 Chapter 10 Part 2

18

10-17) An automobile’s 12 V battery is used to light the automobile’s two headlights.

Each headlight can be modeled as a single resistor. If the two headlights are hooked up to

the battery in parallel to form a circuit, and each headlight is to produce a power of 100

W, what should the resistance of each headlight be?

Need: Resistance, R = ____Ω

Know: Same circuit as Problem 16, but different resistances for the bulbs.

Parallel circuit with two filaments each of R Ω and a 12 V battery.

R

I

12

V

I

1

I

2

V

=

12 V

V

=

0. V

R

10-18) Suppose one of the headlights in problem 10.17 suddenly burns out. Will be the

power produced by the other headlight increase or decrease?

Need: Is P > 100. W or < 100. W?

Know: Circuit is now modified because one leg is burned out. V = 12 volts still

and R1 = 1.4 Ω still.

R

Ω

I

12

V

I

1

I

2

V

=

12 V

V

=

0. V

R

=

∞Ω

10-19) Suppose a car has headlights operating in parallel, but with

different resistances, one of 2.0 Ω and the other of 3.0 Ω. Suppose the

headlight parallel circuit is connected in series with a circuit for a car

drawn from a 12 V battery when both the lights and the stereo are on?

I

Need: Current, I = ____ A

Know: Asymmetric parallel circuit with 2.0 and 3.0 Ω resistor in series with

1.0 Ω resistor all powered by a 12 V battery.

V

12

V

=

I

1

I

2

1.0

Ω

V

0. V

=

12

V

V?

2.0

Ω

3.0

Ω

21

10 -20) Consider the circuit shown below. What are the currents Io through I6? (Hint:

What are the voltages Va and Vb? Note the symmetry between R1/R2 = 5.0/5.0 and R3/R4

= 10.0/10.0.)

12 V

Need: I0, I1, I2, I3, I4, I5, I6, ______A

Know: The circuit has several levels of symmetry so that several of the various

currents are equal by inspection and on the conservation of charge principle.

5.0

Ω

V

12

5.0

Ω

5.0

Ω

10.0

Ω

10.0

Ω

I

5

I

1

I

2

I

3

I

4

I

0

I

6

V

0

V

a

V

b

10-21. Determine the output voltage, Vout, in Figure 10.5 if Vin = 90. V, R1 = 10. ohms,

and R2 = 50. ohms.

Need: Vout = ______ V.

10-22. Use the same RadioShack stock resistors in Example 10.6 to design the

construction of a voltage divider that will reduce the voltage by a factor of 30.

Need: Vout /V1n = 1/30.

Know: 5.0, 10., 15., and 20. ohm resistors in stock

10-23. Use Kirchhoff’s voltage and current laws to determine the voltage drop and

current in each of the three resistors below if R1 = 10. ohms, R2 = 20. ohms, and R3 = 30.

ohms.

Need: V, I in each of R1, R2, & R3.

Know: R1 = 10. ohms, R2 = 20. ohms, and R3 = 30. ohms. And V = 6.0 V

How: Kirchoff’s Laws

10-24. If the resistors in Exercise 10.23 are all equal to 10. ohms (R1 = R2 = R3 = 10.

ohms), what is the current supplied by the 6.0 volt battery?

Need: I = ______A

Know: V = 6.0V and R1 = R2 = R3 = 10. Ω

10-25. Determine the currents I1 and I2 in the current divider illustrated in Figure 10.7 if

V = 50.3 volts, R1 = 125. ohms, and R2 = 375. ohms.

Need: I1 = _____A, I2 = _______A

Know: Vin = 50.3 volts, R1 = 125. Ω, and R2 = 375.Ω

10-26. Repeat Example 10.7 with the resistor R1 changed to 100. Ω and all other values

remain unchanged.

Need: I3 = ______ A

C

D

R

1

100

.

Ω

R

2

28

Know: R1 = 100. Ω, R2 = 20.0 Ω,

R3 = 40. Ω; V1 = 10. V, V2 = 20. V.

10-27. Repeat Example 10.7 with V1 increased to 100.volts and V2 reduced to 5.0 volts.

Need: I3 = ______ A

Know: R1 = 40. Ω, R2 = 20.0 Ω, R3 = 40. Ω; V1 = 100. V, V2 = 5.0

10-28. Determine the currents I1, I2, I3, and I4 in the figure below.

.

Need: I1, I2, I3, and I4

6.0

Ω

12

.

Ω

9.0

Ω

9.0

Ω

i =

5.0

12

. V

10-29. It is the last semester of your senior year and you are anxious to get an exciting

electrical engineering position in a major company. You accept a position from company A

early in the recruiting process, but continue to interview hoping for a better offer. Then your

dream job offer comes along from company B. More salary, better company, more options for

advancement, it is just what you have been looking for. What do you do?

a) Accept the offer from company B without telling company A (just don’t show

up for work).

b) Accept the offer from company B and advise company A that you have

changed your mind.

c) Write company A and ask them to release you from your agreement.

d) Write company B thanking them for their offer and explain that you have

already accepted an offer.

Summarize using an Engineering Ethics Matrix.

1) Apply the Fundamental Canons: Engineers, in the fulfillment of their professional

duties, shall:

1) Apply the Engineering Ethics Matrix

32

Options

Canons

a) Accept B

without telling

A

b) Accept B,

notify A

c) Ask A for

release

d) Refuse B,

stick with A

Hold paramount

the safety,

health and

welfare of the

public.

Does not apply

Perform

services only in

the area of your

competence

Does not apply

Issue public

statements only

in an objective

and truthful

manner

Does not apply

Act for each

employer or

client as faithful

agents or

trustees

Does not apply

Avoid deceptive

acts

No

Yes

Conduct

themselves

honorably …

No

Yes

Solution: The canons narrow down the list of acceptable options to c) and d).

10-30. A female student in your class mentions to you that she is being sexually harassed by

another student. What do you do?

a) Do nothing; it is none of your business.

b) Ask her to report the harassment to the course instructor.

c) Confront the student accused of harassment and get their side of the issue.

d) Talk to the course instructor or the college human resource director on your

own.

Summarize using an Engineering Ethics Matrix.

1) Apply the Fundamental Canons: Engineers, in the fulfillment of their professional

duties, shall:

2) Apply the Engineering Ethics Matrix

Options

Canons

a) Do nothing

b) Ask her to

report

c) Confront

student accused

d) Talk to

course instructor

Hold paramount

the safety,

health and

welfare of the

public.

Does not apply