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Ohm’s Law
Conceptual Relationship
Ohm’s Law
Is usually written down as an equation of the
form:
V = IR
Conceptually, it often makes more sense to
write the equation as:
I = V/R
But what does this actually MEAN in terms of
our circuit???
Current
I is the variable for current.
Current is the flow of electrons through the
wire. You can think of this like cars on a freeway.
The more cars that are going by in a minute, the
more current there is.
Generally, the more energy each electron (or
car) has, the more current there is.
Voltage
• Voltage is the amount of energy given to each
electric charge.
• The voltage comes from the battery and the
battery alone so the other circuit elements do
not affect or CHANGE the voltage.
Resistance
• Resistance is the opposition to the current. This is
anything that makes it harder for current to flow.
• Going back to our freeway example, resistance is
all the things that cause traffic (too many cars at
once, not enough lanes, accidents, the road is in
terrible shape, etc.)
• In the circuit itself, resistance comes from the
resistors, which in our class is usually the light
bulbs. So other circuit elements don’t affect the
resistance.
Back to Ohm’s Law
• Remember, Ohm’s Law is an equation that
expresses the relationship between these three
variables.
• Conceptually Ohm’s Law makes more sense if we
write it like this:
I=V/R
Because voltage is only affected by the battery
and resistance is only affected by the light bulbs.
• CURRENT is being affected by both of voltage
AND resistance – not the other way around.
Back to Ohm’s Law
I=V/R
So if the voltage goes up, say by adding more
batteries, the current will go up too!! Resistance
won’t be affected by this change.
If the resistance goes up, say by adding more
resistors the current will go down. The voltage
would not be affected by this change.