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| AngraMelo:
Ok, first I would like to thank you. You have been tremendously helpful. Having said that, here goes one more question that is bothering me. Im struggling with understanding the phrase: current chooses the path of least resistance. Now imagine a voltage source and in parallel with a light. The current goes through the light and it lights up. Great. Now if I put a resistance in parallel with the light bulb, the lights shines brightly and the resistance heats up. Now imagine the resistance goes short circuit. My intuition says the bulb will not light up given the short. My question is: In the real world most short circuits would still have resistance. So basically the short is a very low resistance, given that the source can give the necessary amps, what/when/how is this threshold where the current stops going to the lightbulb and just goes through the short. I dont understand that Sorry if this is a stupid question |
| Ice-Tea:
As you say, a short circuit still has "some" resistance. In the most cases, it will present several orders of magnitude less resistance and can be considered "zero" for practical purposes. For other cases, you can calculate the current in both parallel sections you calculate for current by using the actual resistance in your calculations. It then becomes a "classic" case of two resistances in parallel. |
| MrW0lf:
--- Quote from: AngraMelo on December 10, 2018, 01:09:40 pm ---Im struggling with understanding the phrase: current chooses the path of least resistance. ... threshold where the current stops going to the lightbulb and just goes through the short. --- End quote --- More correct would be it will distribute proportionally preferring paths of least resistance, so current to bulb will never completely stop. Suggest to play with some (online) circuit simulator. |
| Berni:
Given an ideal battery the lamp would actually never go out, even if you shorted the battery directly at the terminals. Current does chose the path of least resistance but its not deciding what direction it goes into and puts all the current there. Its just a fancy way of saying that more current flows where there is less resistance. If something has half the resistance than the alternative path then twice as much current flows there as a result. Its all just Ohms law. The reason why the lamp goes out when you short the battery is that the battery has a limit of how much current it can provide. As the battery is overloaded the voltage on the terminals drops and if it drops to below the voltage the lamp needs then the lamp goes out. If you had an ideal battery that can supply an infinite amount of current, then the lamp would be unaffected during the short while the wire shorting the battery would quickly start to glow red hot and melt from the massive current flowing trough it. |
| ArthurDent:
Like most sayings, “current chooses the path of least resistance” tries to convey a concept but it isn’t a law and is not precise. Math is the precise language of science and the parallel resistor drawing below will explain what the saying actually means using ohms law. The current I1, flowing through R1 is E/R1. The current I2, flowing through R2 is E/R2. If R1 and R2 are equal then I1=I2 so the current is equal. If R1 is 1 ohm and R2 is 1,000,000 ohms then almost all the current will flow through R1, the 1 ohm resistor, and almost none will flow through the 1,000,000 ohm resistor, or as the saying goes, “current chooses the path of least resistance”. More precisely worded: “most of the current chooses the path of least resistance but the rest of the current will choose the other path”. The drawing below is also simplified but in real life the battery will have some internal resistance and the wiring will have some resistance as well. If the internal resistance of the battery is extremely low then the short circuit current can will be high and if the internal resistance is high then the short circuit current the battery can produce will be low, following ohms law. If you have a small 9 volt battery and you accidently short the terminals probably nothing will happen. If you have a 12 volt auto battery and accidently short the terminals you will probably get an explosion because the extremely low internal resistance means it can produce very high currents. Bottom line is that in all cases ohms law will determine what happens and you have to consider all sources of resistance in a circuit to be precise and predict the effects. |
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