Page 13 - Schaum's Outline of Theory and Problems of Electric Circuits

INTRODUCTION
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Table 1-2 [CHAP. 1
Quantity Symbol SI Unit Abbreviation

electric charge Q; q coulomb C
electric potential V; v volt V
resistance R ohm
conductance G siemens S
inductance L henry H
capacitance C farad F
frequency f hertz Hz
force F; f newton N
energy, work W; w joule J
power P; p watt W
magnetic flux weber Wb
magnetic flux density B tesla T

2
EXAMPLE 1.1. In simple rectilinear motion a 10-kg mass is given a constant acceleration of 2.0 m/s .(a) Find the
acting force F.(b) If the body was at rest at t ¼ 0, x ¼ 0, find the position, kinetic energy, and power for t ¼ 4s.
2
2
ðaÞ F ¼ ma ¼ð10 kgÞð2:0m=s Þ¼ 20:0kg m=s ¼ 20:0N
2
2
2
1
1
ðbÞ At t ¼ 4s; x ¼ at ¼ ð2:0m=s Þð4sÞ ¼ 16:0m
2 2
KE ¼ Fx ¼ð20:0NÞð16:0mÞ¼ 3200 N m ¼ 3:2kJ
P ¼ KE=t ¼ 3:2kJ=4s ¼ 0:8kJ=s ¼ 0:8kW
1.3 ELECTRIC CHARGE AND CURRENT
The unit of current, the ampere (A), is defined as the constant current in two parallel conductors of
infinite length and negligible cross section, 1 meter apart in vacuum, which produces a force between the
conductors of 2:0 10 7 newtons per meter length. A more useful concept, however, is that current
results from charges in motion, and 1 ampere is equivalent to 1 coulomb of charge moving across a fixed
surface in 1 second. Thus, in time-variable functions, iðAÞ¼ dq=dtðC/s). The derived unit of charge,
the coulomb (C), is equivalent to an ampere-second.
The moving charges may be positive or negative. Positive ions, moving to the left in a liquid or
plasma suggested in Fig. 1-1(a), produce a current i, also directed to the left. If these ions cross the
plane surface S at the rate of one coulomb per second, then the resulting current is 1 ampere. Negative
ions moving to the right as shown in Fig. 1-1(b) also produce a current directed to the left.

Table 1-3
Prefix Factor Symbol
pico 10 12 p
9
nano 10 n
6
micro 10 m
3
milli 10 m
centi 10 2 c
deci 10 1 d
kilo 10 3 k
mega 10 6 M
giga 10 9 G
tera 10 12 T