Show The path of least resistance is the physical or metaphorical pathway that provides the least resistance to forward motion by a given object or entity, among a set of alternative paths. The concept is often used to describe why an object or entity takes a given path. The way in which water flows is often given as an example for the idea. DescriptionBicycle traffic barrier used to slow down cyclists circumvented by a detour in the form of a desire path, thereby showing a literal path of least resistanceIn physics, the "path of least resistance" is a heuristic from folk physics that can sometimes, in very simple situations, describe approximately what happens. It is an approximation of the tendency to the least energy state.[1] Other examples are "what goes up must come down" (gravity) and "heat goes from hot to cold" (second law of thermodynamics). But these simple descriptions are not derived from laws of physics and in more complicated cases these heuristics will fail to give even approximately correct results. In electrical circuits, for example, the current always follows all available paths, and in some simple cases the "path of least resistance" will take up most of the current, but this will not be generally true in even slightly more complicated circuits. It may seem for example, that if there are three paths of approximately equal resistance, the majority of the current will flow down one of the three paths. However, due to electrons repelling each other, the total path of least resistance is in fact to have approximate equal current flowing through each path. The reason for this is that three paths made of equally conductive wire will have a total resistance that is one-third of the single path. In conclusion, the current is always distributed over all possible paths inversely proportional to their resistance. The path of least resistance is also used to describe certain human behaviors, although with much less specificity than in the strictly physical sense. In these cases, resistance is often used as a metaphor for personal effort or confrontation; a person taking the path of least resistance avoids these. In library science and technical writing, information is ideally arranged for users according to the principle of least effort, or the "path of least resistance". Recursive navigation systems are an example of this. The path of least resistance applies on a local, not global, reference. For example, water always flows downhill, regardless of whether briefly flowing uphill will help it gain a lower final altitude (with certain exceptions such as superfluids and siphons). In physics, this phenomenon allows the formation of potential wells, where potential energy is stored because of a barrier restricting flow to a lower energy state. See also
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Contrary to popular belief, electricity takes all paths available — in inverse proportion to the impedance of the paths. The magnitude of the current flowing in a path depends on the path's voltage and impedance. The lower the impedance (assuming voltage remains constant), the greater the current. Conversely, the higher the impedance (assuming voltage remains constant), the lower the current. Imagine two unequally sized resistors in parallel. The current flowing through one resistor depends on the size of that resistor — not the one next to it. Assuming an infinite power supply, you could add 1000 resistors in parallel and the current in that one resistor wouldn't change. IEEE Std. 80 uses a value of 1000 ohms for the human body for touch voltage calculations. A 25-ohm ground rod in parallel with a 1000-ohm human will not make an installation any safer from electric shock. For example, if you touch a metal pole energized by a 120V line-to-case fault and there's no effective fault current path, the touch voltage will be enough to kill you — even if you bond the metal pole to a ground rod with a measured ground resistance of 25 ohms. The Figure helps illustrate the following:
For many years, the street lighting and traffic signaling industries used ground rods, without an effective fault current path, to ground metal parts of an electrical system. Electricians thought these installations were safe because “electricity takes the least resistive path, and it bypasses high resistive paths.” Unfortunately, such thinking resulted in several deaths. This thinking still exists. Some equipment installation instructions require a ground rod without an equipment grounding conductor, claiming it's a safe installation. Electricity does take low-resistance paths, including the one of least resistance. But it also takes every other path available to it. You can't suspend Ohm's Law and Kirchhoff's Law by driving 10 ft of copper-clad steel into dirt. To make an installation safe, ensure the touch voltage on metal parts never exceeds 30V for more than a few seconds. You can do this by bonding all metal parts to an effective fault current path in accordance with Art. 250.
There is a very dangerous myth floating around, one which could actually result in severe injury and even death – “Electricity always follows the path of least resistance”. This is one of those myths that results from a general fact being blown way out of proportion. Forget colleges and engineering schools, most high school students learn that electricity does behave this way, as a part of the basics of electricity and resistances. Worryingly, this myth isn’t just stated as a fact, it’s a commonly followed practice in many electrical circuit designs, especially when it comes to grounding. Walk into any industrial plant that uses motors or pumps and you’ll find they’re all connected to ground rods. Ask anyone why that’s done and you’ll likely get the same response everywhere (even from the people in charge of the electrical maintenance) – It’s to eliminate the potential differences. Go Back to the BasicsA motor connected to a grounding cable is supposed to be safe since the electrical path will have lower resistance and electricity will go that way, but there’s something missing here. The theory doesn’t agree with Kirchoff’s Law of Parallel Circuits. That’s right, the same law that is used by electrical students in their first year to calculate the resistance of one resistor connected in parallel with others. Let’s take a look at a basic scenario where two 100Ω resistors are connected in parallel, and you have to calculate the total resistance. Here’s how you’d do it: Total resistance = 1/(1/R1 + 1/R2) Simple really, but to understand why the myth of electricity taking the path of least resistance isn’t strictly true, you need to delve into this a little deeper. If there was a single resistor, the resistance would be 100Ω, but adding another in parallel makes it 50Ω, half the resistance. That’s because the electricity is now flowing through two paths, instead of one. Think of it as water flowing through a 4-inch pipe. Add another pipe in parallel and you get double the flow. How Can This Be Applied to Real-World Scenarios?Let’s take an example of a circuit with 3 resistors of different resistances (20Ω , 300Ω and 600Ω), connected in parallel with a 33-amp current flowing through it. Here’s how the current will be distributed according to the law:
Now, if electricity only takes the path of least resistance, the entire resistance of the circuit should be just 2Ω and all 33 amps should flow through resistor 1. Here’s Why This Happens – Electricity will flow through each and every path available, inversely proportional to the resistance of each path. So, What Does This Mean?Simply put, grounding may reduce the chances of electrocution and a majority of the current will be directed away from your body. However, that’s not all – not by a long shot! Even a proper grounding is just one of the several paths that are available for electricity to take, and consider that: The motor bearings can conduct electricity too, so if someone were to come in contact with the motor with one foot on the ground cable, another path is available – one that goes straight through his or her heart. Electricity always tries to find a path back to the source, which in this case is the supply transformer. The human body typically has an impedance of 100Ω, much lower than that of the dirt between the transformer and the ground rod. If there’s enough stray current, a person standing with a foot on the grounding rod can still be electrocuted. Considering how many times we’ve all heard this particular myth, wrapping your head around this concept might be a little difficult. If you’re still not convinced, try putting all this down on paper so you can follow the reasoning. Draw a circuit with a motor, grounding rod and supply transformer, fill in the values of all the resistances, draw the various parallel paths available for the current, and then you’ll get the picture! D&F Liquidators has been serving the electrical construction materials needs for more than 30 years. It is an international clearinghouse, with 180,000 square facility located in Hayward, California. It keeps an extensive inventory of electrical connectors, conduit fitting, circuit breakers, junction boxes, wire cable, safety switches etc. It procures its electrical materials supplies from top-notch companies across the globe. The Company also keeps an extensive inventory of electrical explosion proof products and modern electrical lighting solutions. As it buys materials in bulk, D&F is in a unique position to offer a competitive pricing structure. Besides, it is able to meet the most discerning demands and ship material on the same day. |