Now let's look at loop two.

Loop two is a lower left-hand loop, and if we start summing the voltages,

starting at the lower left-hand corner of that loop and going around it,

the first one that we encounter is 2 milliamp source.

We really don't know what the voltage drop is across that, and

we can't use Ohm's law to determine it.

So we could, in our mesh equation, introduce another variable and

maybe call it V 2 milliamps for this current source.

But that would add another unknown to our set or unknowns.

Right now, we have unknown I1, unknown I2 and unknown I3.

If we can determine those three,

then we can find any other parameter thst we want in our circuit.

What if we introduce this additional variable?

That's four variables that we have.

But we're only going to have three loop currents or three mesh currents.

So we would have more unknowns than we do equations, and

we wouldn't be able to solve our problem.

So we know that, when we're using mesh analysis to solve problems,

what we're looking for are the mesh currents, I1, I2, and I3.