I learnt in one of my classes that “current flows in the path of least resistance” but how does the current know which path is least resistant?
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“How does it know this?” is one of the most persistent questions here and the answer is usually that what we are talking about is a physical phenomenon, has no brain, and doesn’t think. Trying to imagine that it thinks is what makes the question hard to answer.
In this case it’s the same reason why you don’t float into space and leave the planet: gravity is a force acting on your body and it pulls you towards the Earth. Your feet don’t “know how to stick to the ground”, your body is being pulled towards it! The same kind of phenomenon is how electricity behaves.
Electricity in wires is a lot like water in pipes, and that’s easier to visualize. Imagine I have a water hose and I put a splitter at the end. Normally this means 50% of water will go to the left and 50% will go to the right. Now imagine I attach an adapter to the left side that funnels its water through a smaller hose, like a drinking straw. If we do this and measure how much water is coming out of each side, we’ll see that while there’s a strong stream of water coming out of the left-side straw there’s more total water coming out of the right-side hose. Why?
Well, the water coming out of the faucet is trying to push all the water in front of it further down the hose. When it pushes on water at the splitter, it tries to push water both ways.
The left side fills up with water very quickly because the drinking straw is small. Once it fills up, to put more water into the straw involves pushing the water already inside of it out. This takes a bit of effort, so if we were drawing a Physics diagram we’d say the water in the straw is pushing back a little bit against the water in the hose. But since there’s a lot more water behind the straw than in front of it, the hose wins.
The right-side hose doesn’t fill up with water as fast. That means while the straw is pushing back a little bit, the right-side hose can still easily take on water and isn’t pushing backwards.
So what’s happening is while 50% of the water still TRIES to go into the straw, since the water in the full straw pushes back not all of that 50% gets to go inside. It’s still being pushed, so it gets pushed over to the right side where there is less water pushing backwards. That means by making the left side smaller, I caused extra pressure in the hose that makes more than 50% of the water go out of the right side. Nothing is thinking. Stuff’s just getting pushed and going where it gets pushed.
ALL of that is how wires work. Lower resistance paths are like bigger hoses: they can “fit” more electricity before they start pushing back. Higher resistance paths are like smaller hoses: they “fill up” and start pushing back faster. So when electricity is being pushed and two paths exist, less electricity flows along paths with higher resistance. Just like how if I clog up a hose no water can move through it, some materials like rubber push back so hard no electricity can flow through them. And if we set it up so there’s one wire with high resistance and one wire with low resistance, we see it like my straw and hose example where *some* electricity goes through the high resistance wire but *most* of it goes through the low resistance wire.
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