Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

Every engineer needs to understand the fundamentals of electricity and magnet-

ism. Look around, and you will see all the devices, appliances, and machines that are

driven by electrical power. The objective of this chapter is to introduce the funda-

mentals of electricity. We will briefly discuss what is meant by electric charge, electric

current (both alternating current, ac, and direct current, dc), electrical resistance, and

voltage. We will also define what is meant by an electrical circuit and its components.

We will then look at the role of electric motors in our everyday lives and identify the

factors that engineers consider when selecting a motor for a specific application.

As explained in Chapter 6, based on our understanding of our physical world today,

we needseven fundamentalorbase dimensionsto correctly express the physical laws

that govern our world. They arelength, mass, time, temperature, electric current,

Electric Current and Related Parameters 345

TABLE 6.7 Fundamental Dimensions and How They Are Used in Defining Variables that Are Used in Engineering Analysis and Design

Fundamental

Dimension Related Engineering Variables

Length (L) Radian , Area (L

2

) Volume (L

3

) Area moment

[Chapter 7] Strain of inertia (L

4

)

Time (t) Angular speed ,

[Chapter 8] Angular acceleration Volume flow rate

Linear speed ,

Linear acceleration

Mass (M) Mass flow rate , Density ,

[Chapter 9] Momentum Specific volume

Kinetic energy

Force (F) Moment (LF), Pressure ,

[Chapter 10] Work, energy (FL), Stress , 1

F

L^22

1

F

L^22

1

ML^2

t^22

1

L^3

(^1) M 2
ML
t^2
1
M
(^1) L^32
M
t^2
1
L
t^22
1
L
t^2
1
L^3
(^1) t 2
1
t^22
1
1
t^2
1
L
L^2
1
L
L^2
Linear impulse (Ft), Modulus of Specific weight ,
Power elasticity ,
Modulus of
rigidity
Temperature (T) Linear thermal expansion Volume thermal
[Chapter 11] expansion
Specific heat
Electric Current (I) Charge (It) Current density
[Chapter 12] 1
I
L^22
1
FL
MT^2
1
L^3
(^1) L (^3) T 2
L
LT^2 ,
1
F
L^22
1
F
(^1) L 22
FL
t^2
1
F
L^32
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