Now let's discuss Ohm's law which will be a natural lead-in
from the discussion of how the resistance is defined.
And is in fact, just a rearranging of the equation we just introduced for the resistance.
So just by multiplying both sides of the equation for resistance
by the resistance we have an equation that looks like this,
we have V equals IR this is telling us that the voltage equals the current times the resistance
but which voltage current and resistance is this.
If you look at a circuit like this one,
it's a very simple circuit we have a voltage being applied,
that voltage is pushing current through a resistor
and we symbolize resistors by the symbol that I've been showing here,
which is a sort of a jagged line and its anything in your circuit
that is trying to slow down the flow of the current as it goes through your circuit.
So this is a resistor, and we say it has some resistance some resistance R in this case.
What Ohm's Law is telling us, is that if we have a particular amount of current
flowing through our resistor, the resistor is going to lower the pressure
or the amount of push that we have for our electricity
by some quantity, and that quantity by which we drop the voltage
as we go from one side of the resistor to the other
as we move through the resistor is equal to the current going through the resistor
times the resistance of the resistor.
So this is Ohm's law, the voltage drop is equal to the current times the resistance.
The current in this case, as we saw what the circuit, the fluid flow situation rather
is the adaptable quantity, in other words for a given circuit we have some voltage.
We have some pump if you will, some actual battery
and we also have a given amount of resistance.
So those are sort fix physical quantities,
which means that the variable that can adapt to the physical situation
that you have given it, is the current.
So usually, what's happening in a problem like this
is we know we have a particular voltage, we know we have introduced some particular resistance,
and when we would like to find what the resulting current will be,
given this physical system that we've introduced.