After
reading this section you will be able to do
the following:
Identify
Ohm's law and discuss why it is important.
Calculate
the amount of electric current in a circuit using Ohm's law.
Probably the most important mathematical
relationship between voltage, current and resistance in electricity
is something called “Ohm’s Law”. A man named George
Ohm published this formula in 1827 based on his experiments with
electricity. This formula is used to calculate electrical values
so that we can design circuits and use electricity in a useful
manner. Ohm's Law is shown below.
OHM'S LAW
I
= V/R,
I = current,
V = voltage, and R =
resistance
*Depending on
what you are trying to solve we can rearrange it two other
ways.
V
= I x R
R = V/I
*All of these
variations of Ohm’s Law are mathematically equal to
one another.
Let’s look at what Ohm’s
Law tells us. In the first version of the formula, I = V/R, Ohm's
Law tells us that the electrical current flowing in a circuit
is directly proportional to the voltage and inversely proportional
to the resistance. In other words, an increase in the voltage
will tend to increase the current while an increase in resistance
will tend to decrease the current.
The second version of the formula
tells us that if either the current or the resistance is increased
in the circuit, the voltage will also have to increase. The third
version of the formula tells us that an increase in voltage will
result in an increase in resistance but that an increase in current
will result in a decrease in resistance.
As you can see, voltage, current,
and resistance are mathematically, as well as, physically related
to each other. We cannot deal with electricity without all three
of these properties being considered.
(The symbol for an Ohm
looks like a horseshoe and is pictured after the "100"
in the diagram above.)
Review
Ohm's
Law is used to describe the mathematical relationship between
voltage, current, and resistance.
