Video: Eg17S1-Physics-Q3A

Name one factor that can increase the electrical resistance of a copper wire at a certain temperature.


Video Transcript

Name one factor that can increase the electrical resistance of a copper wire at a certain temperature.

Say that we have a wire made of copper and that this wire has a resistance we can call capital 𝑅. That resistance 𝑅 tells us just how difficult it is for a charged particle, an electron, to move down the length of the wire. That resistance happens in large part because these electrons, as they move along, keep crashing into atoms in the copper wire. Nonetheless, if all goes well, the electrons make it across the copper wire.

We want to consider here how we could increase the resistance of a copper wire, given that it’s fixed at a certain temperature. If we continue to think in terms of electrons running into atoms in our current-carrying wire, we start to see there’re changes we could make to this wire that indeed would make it harder for the electrons to get from one end to the other. For example, what if we made the wire longer than it was originally. In this case, a travelling electron has many more collisions with atoms in this copper material to endure before it makes it to the end of the wire. In other words, the resistance of the wire has increased because it’s longer.

But there’s another change we could make to our copper wire, which would have a similar effect, increasing resistance. What if, instead of making our wire longer, we just made it thinner. We decreased its diameter. In this case, there’s simply less space in the conductor for current to occupy as it travels. To see how this increases resistance, let’s consider an analogy. Imagine being in a very large field with lots of people, where each one of these dots represents a person standing in the field. And imagine further that, at one end of the field, there’s a wall with a very narrow walkway in the middle of the wall that people could access.

Imagine what would happen if everyone in the field decided that they wanted to leave the field and walk down this narrow walkway. As people moved towards this walkway, there would be a traffic jam, right. Well, the same thing happens when we make our wire that carries electrons very narrow. Only a fraction of the electrons could travel down the wire at any one time. So the resistance of the wire has effectively gone up. Here’s what we can say then about factors that increase the electrical resistance of this copper wire. We can increase resistance 𝑅 by increasing the wire length or decreasing the wire cross-sectional area.

So the length of the wire as well as its cross-sectional area are both factors that we can change to increase the electrical resistance of the wire.

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