Video Transcript
Any wire will have some amount of
electrical resistance. There are two unequal lengths of
identical wire. Which one of the following
sentences is correct? (A) Both wires have the same
resistance. (B) The wire of greater length has
the greater resistance. (C) The wire of greater length has
the lower resistance.
Okay, let’s say we have two bits of
wire here. And in every way, these wires are
the same. That is, they’re made of the same
material, they had the same diameter, and so on. Except, as we can see, one wire is
longer than the other. We want to compare the electrical
resistances of these wires. Imagine we get two identical
batteries, and we connect up one battery to each wire. This will cause electrical charge
to flow to each wire and then through each one.
But here’s the thing. The wires resist the flow of
charge. They make it harder for current to
pass through the circuit. We can think of this resistance
being caused by the material in the wire getting in the way of the moving
charge. The more material there is in front
of the moving charge, the harder it is for the charge to move forward. That means the charge passing
through the shorter wire has to get through this amount of resistive material. But then, the charge passing
through the longer stretch of wire has to get through this much material. The longer section of wire is
harder for charge to pass through. That means it has a greater
resistance. We choose answer option (B). The wire of greater length has the
greater resistance.
