Another important relationship may be seen by studying figure 17. Thus far,

power has been calculated with voltage and current (P2 = E x I), and with

voltage and resistance

FIGURE 17.

GRAPH OF POWER RELATED TO CHANGING CURRENT

Referring to figure 16 on page 33, note that power also varies as the square

of current, just as it does with voltage. Thus, another formula for power,

with current and resistance as its factors is P = I2R. This can be proved

by:

Since:

E=IxR

By substitution in:

P=ExI

You get:

P=IxRxI

Or:

P= I x I x R

p = I2R

Therefore:

Up to this point, four of the most important electrical quantities have been

discussed. These are voltage (E), current (I), resistance (R), and