20 volts + (I x 60 Ohms) + (-180 volts) + 40 volts + (I x 20 Ohms) = 0

20 volts - 180 volts + 40 volts 4 (C x 60 Ohms) + (I x 20 Ohms) = 0

-120 volts + (I x 80 Ohms) = 0

I x 80 Ohms = 120 volts

I = 1.5 amps

4.

Circuit Terms and Characteristics

Before you learn about the type of circuits other than the series circuit,

you should become familiar with some of the terms and characteristics used

in electrical circuits.

These terms and characteristics will be used

throughout your study of electricity and electronics.

a. *Reference Point. * A reference point is an arbitrarily chosen point

to which all other points in the circuit are compared. In series circuits,

any point can be chosen as a reference and the electrical potential at all

other points can be determined in reference to that point. In figure 33, on

the following page, point A should be considered the reference point. Each

series resistor in the illustrated circuit is of equal value. The applied

voltage is equally distributed across each resistor. The potential at point

B is 25 volts more positive than at point A. Points C and D are 50 volts

and 75 volts, more positive than point A respectively.

When point B is used as the reference, as in figure 34 on the following

page, point D would be positive 50 volts in respect to the new reference

point.

The former reference point A, is 25 volts negative in respect to

point B.

As in the previous circuit illustration, the reference point of a circuit is

always considered to be at zero potential. Since the earth (ground) is said

to be at a zero potential, the term ground is used to denote a common

electrical point of zero potential. In figure 35, on page 60, point A is

the zero reference, or ground, and the symbol for