** Next:** Other types of energy
**Up:** Potential Energy
** Previous:** Elastic or Spring Potential

##

Electrical Potential Energy

A third type of potential energy we mention is that due to the electrical
force - this is the force of attraction between electric charges
that causes that annoying static cling in your dryer. We will discuss
this in more detail in Chapter 9 - for now, we only mention that the
``voltage'' of a car battery or household outlet is actually a measure of
the electrical potential energy between two terminals.
On your electric bill one can find the number of ``kilowatt-hours'' of
electricity that has been used in a month - this is a measure of the
electrical energy that has been consumed. A kilowatt-hour (kW-hr) is
defined as

According to this definition, we see that 1 kW-hr is a unit of energy, which
can be expressed in Joules by multiplying the power (1000 W) by the time
(1 hour = 3600 seconds) so that

Thus, for example, burning a 120 W light bulb for 100 hours will consume
120 W x ( 1 kW / 1000 W ) x 100 hr = 12 kW-hr, which is about 43 million
Joules.
If electricity is charged at a rate of $0.08 per kW-hr, this would cost
12 x $0.08 = $0.96. Clearly the cost of electricity would seem even more
reasonable if expressed in terms of Joules.

** Next:** Other types of energy
**Up:** Potential Energy
** Previous:** Elastic or Spring Potential
*modtech@theory.uwinnipeg.ca *

1999-09-29