132 votes

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 ...
  • 7,074
108 votes

Intuitively, why does putting capacitors in series decrease the equivalent capacitance?

Can someone please explain, intuitively (without any formula, I understand the formulas), why the equivalent capacitance of capacitors in series is less than the any individual capacitor's ...
  • 58.2k
89 votes

Birds on a wire (again) - how is it that birds feel no current? They are just making a parallel circuit, no?

A birds legs are pretty close together. An electrical transmission wire has very little resistance. This means that the voltage as a function of distance barely changes. So the voltage difference ...
  • 14.9k
71 votes
Accepted

In what order would light bulbs in series light up when you close a long circuit?

I'm assuming that you're imagining a long, skinny, series circuit with three simple resistive lamps, like this: ...
  • 75.6k
61 votes

Is the voltage ever undefined?

The voltage between to points in the universe is always defined. But the voltage between two circuits is undefined because (at least from electronics point of view) circuits are abstract models of ...
  • 631
60 votes

If electrons are identical and indistinguishable, how can we say current is the movement of electrons?

Perhaps you're visualizing the electron flow as if it were a series of snapshots, timed so that the snapshots all look identical. But it's more than that. The wavefunction of a moving electron is ...
  • 24.2k
58 votes
Accepted

Why does nature prefer simultaneous events?

None of the processes you describe are instantaneous. Acceleration is produced without any delay on applying force. Angular acceleration is produced without any delay on applying torque. If you ...
  • 53.8k
53 votes

Could someone intuitively explain to me Ohm's law?

In addition to the other answers, here is something for the intuition: $$V=RI$$ More "pressure" $V$ (more correctly: higher "pressure" difference from one side to the other) is required to keep the ...
  • 47.4k
53 votes
Accepted

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^...
  • 1,637
51 votes

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 ...
  • 9,897
50 votes

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. ...
  • 641
48 votes
Accepted

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 ...
  • 3,722
48 votes

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 ...
  • 1,178
47 votes

When jumping a car battery, why is it better to connect the red/positive cable first?

This is more of an automotive question but... The reason you connect the reds first is to minimize the likelihood of a short. Remember that you're typically in control of one clip at a time, so one ...
  • 43.2k
46 votes

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 ...
  • 3,038
46 votes

Why doesn't the voltage increase when batteries are connected in parallel?

tl;dr Batteries do not create electric fields to move charges. They move charges, which creates electric fields. a battery [...] gives out some electric field that moves through the circuit and gives ...
  • 561
45 votes
Accepted

What happens to an inductor if the stored energy does not find a path to discharge?

Suppose an inductor is connected to a source and then the source is disconnected. The inductor will have energy stored in the form of magnetic field. But there is no way/path to discharge this ...
43 votes

Birds on a wire (again) - how is it that birds feel no current? They are just making a parallel circuit, no?

Let me say in advance: You are perfectly right! The wire is a resistor, the bird is a resistor, and a bird standing on a wire with both feet down is indeed a parallel resistor to the wire. This means ...
41 votes
Accepted

The water analogy seems to imply that power = current. Why is this incorrect?

Power to a water-wheel depends both on the current (amount of water delivered) and the head (vertical drop of water as it turns the wheel). So, the water analogy does have TWO variables that ...
  • 9,170
41 votes

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. ...
  • 70.4k
39 votes

What is the physical explanation for energy transport in simple electrical circuits?

How is energy transported at the speed of light if electrons don't flow like very fast water? Let me reply with the hydraulic analogy, i.e. with replacing electrical current by water flow. Open ...
38 votes
Accepted

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 ...
  • 3,486
37 votes
Accepted

What happens if you use a battery to charge up a capacitor fully, and then disconnect the battery, where does the charge 'go'?

The charge won't go anywhere and the capacitor will remain charged until you short the plates of the capacitor. Where there was once a battery terminal there is now an insulator and that stops the ...
  • 1,467
36 votes
Accepted

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 ...
  • 7,785
35 votes

Is every open circuit a capacitor?

You are right, every circuit possesses some unintended capacitance, which is called "stray" capacitance. Whether or not it affects the operation of the circuit depends on the frequencies that the ...
35 votes

What happens to an inductor if the stored energy does not find a path to discharge?

It depends. You cannot disconnect an ideal inductor from an ideal voltage source with an ideal switch. These ideal things will break your calculations and you will get an infinite voltage on ...
  • 6,113
35 votes
Accepted

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 ...
  • 4,418
34 votes
Accepted

Are the plates of a battery really charged?

I think that most confusion about batteries comes from ignoring the electrolyte. For example: Zinc has 2 valence electrons. So it wants to get rid of them. To do so it sends them to the copper ...
  • 70.4k
34 votes
Accepted

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 ...
  • 70.4k
33 votes
Accepted

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. ...

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