Fundamental Engineering Concepts - Mathematics and Statistics for the Environment - page 269

The voltage ( E 3 ) across R 3 is

E 3 = I × R 3

E 3 = 1.43 amps × 30 ohms = 42.9 volts

The power dissipated by R 1 is

P 1 = E 1 × I

P 1 = 28.6 volts × 1.43 amps = 40.9 watts

The power dissipated by R 2 is

P 2 = E 2 × I

P 2 = 28.6 volts × 1.43 amps = 40.9 watts

The power dissipated by R 3 is

P 3 = E 3 × I

P 3 = 42.9 volts × 1.43 amps = 61.3 watts

The total power dissipated is

P T = E T × I

P T = 100 volts × 1.43 amps = 143 watts

Note: Keep in mind when applying Ohm's law to a series circuit to consider whether the values
used are component values or total values. When the information available allows the use of
Ohm's law to find total resistance, total voltage, and total current, then total values must be
inserted into the formula.

To find total resistance:

E
I

T
T

R =

T

To find total voltage:

E T = I T × R T

To find total current:

E
R

T
T

I =

T

11.7.6.6 Kirchhoff's Voltage Law
K i r ch h of f 's voltage law states that the voltage applied to a closed circuit equals the sum of the volt-
age drops in that circuit. It should be obvious that this fact was used in the study of series circuits to
this point. It was expressed as follows: