# Tag Info

### Why doesn't current pass through a resistance if there is another path without resistance?

The basic circuit theory "rules" you imply, are high level simplifications applicable at a large scale and at slow speeds. If you look at it close and fast enough, you could say that a current really ...
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### Why do we use AC for long distance transmission?

The first point to make is: We don't always use AC. There is such a thing as high voltage DC for long-distance power transmission. However its use was rare until the last few decades, when relatively ...
• 1,111

### On this infinite grid of resistors, what's the equivalent resistance?

This is the XKCD Nerd Sniping problem. It forced me to abandon everything else I was doing to research and write up this answer. Then, years later, it compelled me to return and edit it for clarity. ...
• 801
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### What *exactly* is electrical current, voltage, and resistance?

Before explaining current, we need to know what charge is, since current is the rate of flow of charge. Charge is measured in coulombs. Each coulomb IS a large group of electrons: roughly 6.24 ˟ 10^...
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### Will the volt, ampere, ohm or other electrical units change on May 20th, 2019?

Late last century electrical standards based on Josephson junctions became common. A Josephson junction together with an atomic clock can give an exquisitely precise voltage standard in terms of the ...
• 104k

### Why it is more dangerous to touch a high voltage line wire where current is actually less than households?

Current flowing in the wire is irrelevant to the danger. It's the current flowing through your body that will hurt you, and the amount of current that flows through your body will be proportional to ...
• 15.3k
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### Why doesn't Kirchhoff's Law work when a battery is shorted with an ideal wire?

Just to complement the other answers: This isn't really about Kirchhoff's law. Rather, it is about an idealised situation that does not have a solution at all. When you draw such a diagram, you can ...
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### Where is the energy coming from to light my Christmas tree lights?

Here's what I think: It doesn't take a lot of charge to light LEDs for a few hours. Your "Solar Battery" probably still has enough charge from the factory to power the lights for a while. I ...
• 1,302

### Why doesn't current pass through a resistance if there is another path without resistance?

I'll try to offer a simpler analogy of how that works. Camp A on the side of a mountain is full of hikers. There is another empty campsite B on the other side of the mountain. And there are two ...
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### Why don't we get a shock touching neutral wire?

Do not touch even the neutral wire in a live circuit! There are numerous failure modes that could make you dead wrong about not getting shocked. The neutral wire does have current going through it. ...
• 104k
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### What happens to the resistance of a wire if it is heated up?

Either one can be true depending on the material. In metals, the electrons don't need any additional energy to move, so the main effect of temperature is to cause the atoms to vibrate more, which ...
• 10.9k

### Why do we reduce only current to prevent power loss? Why not voltage?

You need to pay attention to where the voltage is. Increasing the supply voltage does not mean that the voltage in all parts of the circuit go up. In fact, it might go down in some parts. Let's do ...
• 2,075
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### Are the "bird sitting on a live wire" answers wrong?

Which explanation is more correct? The answer to the second question you cite is the best one. In order to be "electrocuted" a non-trivial amount of current must flow through the body. The ...
• 3,989
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### Calculating equivalent resistance

I am used to smoothing out badly shaped circuits by pulling the wires: Then I get a better circuit by cutting the extra wires: So there are three resistors in parallel, indicating that the current ...
• 4,580
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### What is the point of a voltage divider if you can't drive anything with it?

Oh, but you can. You can drive an high impedance input with it...including a buffer, which can then in turn be used to drive whatever you want. The more current you draw the more the voltage will ...
• 9,319
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### Why is conductivity defined as the inverse of resistivity?

In my experience this comes from resistance and conductance in electrical engineering and circuit theory. If you use the loop current analysis method on a circuit of resistors and sources then you get ...
• 104k
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### Clarification of the concept "less resistance means less heating" in a wire

They’re describing the situation where the wires are carrying power to a load. It’s the load that (mostly) determines the current in the wires leading to it. A $1200$W oven on $120$V needs $10$A. ...
• 14.6k

### Is everything a resistor?

resistance is due to collision with protons Actually, there are lots of materials which don't contain protons outside of atomic nuclei — e.g. steel, glass, oxygen — but all these do have resistance. ...
• 29.1k

### Does a Mobius resistor have zero inductance? How would you calculate the inductance?

The inductance can be calculated, but it is first necessary to look at the behavior at very fast timescales of a ns or so. Clearly the two faces of the strip form a transmission line and so, at short ...
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### Why is conductivity defined as the inverse of resistivity?

The usual definition matches up with calculations with parallel resistors. For example, the total resistance of two parallel resistors is $$\frac{1}{R} = \frac{1}{R_1} + \frac{1}{R_2}.$$ If the ...
• 24.2k
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### How will the current flow in the figure drawn below?

An approximate numerically calculated figure is attached. The figure is a two-dimensional result. Although 3D calculations is possible, the figure is easier to see in 2D. $\phi$ is potential in volts. ...
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### Does Ohm's law hold in space?

But in space the resistor doesn't have anywhere to put off the heat! Actually, it does. Heat transfer can occur by three means: conduction, convection, and radiation. Very basically, heat conduction ...
• 807

### How do electrical devices limit the current flow from a socket?

Your home circuit does not "know" how much current to deliver to each socket or appliance. The circuit supplies a constant voltage, and it is then up to each appliance to limit the current ...
• 56.9k

### What is the electrical difference between rolled and unrolled extension cables?

The reason it is better to unroll the cable is because it improves its ability to dissipate heat, which could be important for heavy loads, i.e., when the cable could potentially become hot. The role ...
• 12.2k

### Why isn't current carried through a vacuum?

As you noted, particle accelerators are examples of electric currents flowing though a vacuum. In order to answer why a vacuum is considered an insulator, you have to consider where the charged ...
• 24.2k

### How is silver a better conductor than platinum?

The situation is a lot more complicated than you described. When calculating the conductance of a metal, you first need to evaluate the allowed energy states of electrons in the bulk material, which ...
• 10.4k

### Why do we use AC for long distance transmission?

The reason we use AC is that the AC voltage is easily changed using a transformer. To change DC voltage requires complex and inefficient circuitry. Suppose you are sending some power $P$ from the ...
• 358k
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### How do resistors generate different heat if we make the current fixed and changed the voltage and resistance? Notice the flow of charge is constant

Your initial circuit is like this: So you get 2A flowing and a power of 20W dissipated in the resistor. Then you double the voltage and the resistance: The two batteries add up to single source of ...
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