. Where did the P=IV equation come from?
Please join me for a mathematical interlude.
Voltage is work/charge or
.
We earlier defined
.
W = qV so we can write Power as
.
The q/t or charge per unit time is the same as current, I.
The equation now becomes P=IV.
Why are we charged in kilowatt hours?
Remember that power is work divided by time. If we multiply power times time we are left with work or the energy we used.
How much does it cost to leave a 75 watt light bulb on all day if the cost
of energy is $0.12/kWh?
A 75 watt bulb is a .075 kilowatt bulb.
(
)
Cost = ($0.12/kWh)(0.075 kW)(24 h) = $0.216 or 22 cents.