Figure 2.18: The 6V and 8V sources add to 10V with the help of trigonometry.
In the next section, we’ll learn how to represent vector quantities in symbolic rather than graphical
form. Vector and triangle diagrams suffice to illustrate the general concept, but more precise
methods of symbolism must be used if any serious calculations are to be performed on these quantities.
• REVIEW:
• DC voltages can only either directly aid or directly oppose each other when connected in series.
AC voltages may aid or oppose to any degree depending on the phase shift between them.
2.5 Polar and rectangular notation
In order to work with these complex numbers without drawing vectors, we first need some kind of
standard mathematical notation. There are two basic forms of complex number notation: polar and
rectangular.
Polar form is where a complex number is denoted by the length (otherwise known as the magnitude,
absolute value, or modulus) and the angle of its vector (usually denoted by an angle symbol
that looks like this: 6 ). To use the map analogy, polar notation for the vector from New York City
to San Diego would be something like “2400 miles, southwest.” Here are two examples of vectors
and their polar notations: (Figure 2.19)
Standard orientation for vector angles in AC circuit calculations defines 0
o as being to the right
(horizontal), making 90o
straight up, 180o
to the left, and 270o
straight down. Please note that
vectors angled “down” can have angles represented in polar form as positive numbers in excess of
180, or negative numbers less than 180. For example, a vector angled 6 270o
(straight down) can
also be said to have an angle of -90o
. (Figure 2.20) The above vector on the right (7.81 6 230.19o
)
can also be denoted as 7.81 6 -129.81o
.
Rectangular form, on the other hand, is where a complex number is denoted by its respective
horizontal and vertical components. In essence, the angled vector is taken to be the hypotenuse of a
right triangle, described by the lengths of the adjacent and opposite sides. Rather than describing
a vector’s length and direction by denoting magnitude and angle, it is described in terms of “how
far left/right” and “how far up/down.