Let us consider an element in an electrical circuit through
which a current I is flowing. Suppose there is a potential difference V
across this element, and in a time
t
a charge
Q
passes by. The work
W
done by the electric field in moving this charge is given by,
W
= V
Q
. Thus, the work done per unit time, or the power P, is
|
|
P
=
|
(5) |
We recall the units of power are J/s, or Watts (W).
Electrical utilities normally bill on the basis of kilowatt-hours (kWh), which is the amount of energy the consumer has used in a given time period. One can convert kWh to J by the following formula:
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|
1
kWh = 1000 Wh = 1000
|
(6) |
