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145 votes

Why is there no magnetic field around a wire connected to electricity at home?

There are two wires, the second wire carries the equal (!) return current. The magnetic fields from the two wires cancel out, except at very short distance. For measuring the current from the field ...
StessenJ's user avatar
  • 1,506
101 votes

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 ...
Jamie Hanrahan's user avatar
99 votes

Is electricity really the flow of electrons or is it more involved?

The idea that electricity "does not exist" is just verbal sophistry along the same lines as "matter does not exist, it is frozen energy" or, "you do not exist, you are a ...
Guy Inchbald's user avatar
  • 7,410
96 votes

If water is not a good conductor, why are we advised to avoid water near electricity (no wet hands near circuits etc.)?

"Pure" water is a very poor conductor (resistivity is actually used as a measure of purity). "Real" water is not pure - it contains electrolytes and is quite conductive. Also - ...
Floris's user avatar
  • 119k
96 votes

Why doesn't the brightness of a bulb change with time?

Two reasons: An incandescent bulb glows not (directly) because it has electricity going through it, but because it is hot. Even when the power going through the bulb decreases, it takes some time for ...
Chris's user avatar
  • 17.2k
92 votes

Hypothetically, why can't we wrap copper wires around car axles and turn them into electromagnets to help charge the batteries?

This is basically what happens in the alternator. The car's engine, which turns the wheels, also turns the alternator's rotor. The magnetic rotor is surrounded by coils of wire, and induces a current ...
Technically Natural's user avatar
87 votes

Why are the electric force and magnetic force classified as electromagnetism?

Consider this: A charged particle at rest creates an electric field, but no magnetic field. Now if you walk past the charge, it will be in motion from your point of view, that is, in your frame of ...
garyp's user avatar
  • 22.4k
75 votes

Hypothetically, why can't we wrap copper wires around car axles and turn them into electromagnets to help charge the batteries?

Yes. This is how regenerative braking works. There is a style of brakes that is used in many electric or hybrid cars that, rather than converting the motion of the wheels into heat energy the way ...
nick012000's user avatar
  • 1,309
71 votes

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: ...
rob's user avatar
  • 90.7k
71 votes

Do solar panels act as an electrical load on the sun?

There is no electrical connection between our solar panels and the Sun. The Sun radiates electromagnetic energy (photons) out into space. If we catch some of those photons, the Sun neither knows nor ...
Solomon Slow's user avatar
  • 14.6k
69 votes

Why can no other chemical elements be used for making a light bulb filament?

Essentially: carbon, osmium, tantalum, and tungsten, along with rhenium, are the only (known, stable) elements that have melting points high enough to remain solid at the high temperatures required to ...
abeta201's user avatar
  • 676
62 votes

Can a gym be built to supply electricity to homes?

The maximum continuous power that can be generated for an hour by a fairly fit person on an efficient machine like an exercise bike or rowing machine is $\sim 200$ W (olympic-standard track cyclists ...
ProfRob's user avatar
  • 132k
61 votes

Is electricity really the flow of electrons or is it more involved?

Electricity is not a well-defined term in physics. It's a layman's term that means something like what physicists call electrical phenomena. However it also gets used (like your first link says) for ...
The Photon's user avatar
  • 27.9k
57 votes

Why can electric cars recoup energy from braking, but a spaceship cannot?

The main point is that the space-ship is a closed system and the car is not Consider that to conserve momentum we need to give something else the momentum our decelerating object had before. In the ...
Lio Elbammalf's user avatar
55 votes

Speed of light vs speed of electricity

The speed of electricity is conceptually the speed of the electromagnetic signal in the wire, which is somewhat similar to the concept of the speed of light in a transparent medium. So it is normally ...
safesphere's user avatar
  • 12.7k
51 votes

How did physicists know that there are two kind of charges?

Get together a collection of charges. As many different ways to generate a charge as you can think of. Go ahead and invite your friends so they can think of some more. (As a practical matter you make ...
dmckee --- ex-moderator kitten's user avatar
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 ...
Solomon Slow's user avatar
  • 14.6k
48 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 ...
Cort Ammon's user avatar
  • 49.7k
45 votes

Why do gases conduct at low pressure?

At high pressure, the mean free path of electrons is quite low. The electrons don't get enough time to get accelerated. If the electrons don't accelerate for long, they can't gain the high velocity or ...
Yashas's user avatar
  • 7,193
45 votes

Why doesn't the brightness of a bulb change with time?

We already have great answers, but I'll add an anecdote to this: I once played around with several light sources and a scientific camera. The overall experiment was not overly scientific, and I only ...
NightLightFighter's user avatar
44 votes

What does the notation $8.9875517923(14)$ mean?

It's the uncertainty in the last two digits: $$8.9875517923(14) = \color{blue}{8.987\,551\,79}\color{red}{23} \pm \color{blue}{0.000\,000\,00}\color{red}{14}. $$
SuperCiocia's user avatar
  • 24.8k
44 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. ...
Dale's user avatar
  • 102k
44 votes

Why don’t nuclear reactors burn through most of their fuel before discarding it?

The most important limit is that you can't separate the byproducts from the fuel without reprocessing. Among the byproducts are neutron-absorbers, which poison the desired controllable reaction. ...
BowlOfRed's user avatar
  • 40.4k
43 votes

Why do metals have free electrons?

Without getting into the quantum mechanical details, here’s a cartoon depiction of what’s going on. The vertical axis represents energy. Like other answers have already pointed out, metals don’t have ...
Superfast Jellyfish's user avatar
42 votes

Is there a liquid which boils at room temperature and normal pressure, and can we use it to produce electricity?

I'm going to answer the implicit question instead of the explicit one. The implicit question is, if we had such a liquid, would this be a good idea? Let's first talk about power stations in general. ...
N. Virgo's user avatar
  • 34.1k
40 votes

How can electric fields be used to detect cracks in metals?

Cracks and other flaws can be found in metal parts by scanning the surface of the part with a small electromagnetic coil, which induces a current flow in the metal part as if the coil and the part ...
niels nielsen's user avatar
40 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 ...
Thomas Fritsch's user avatar
38 votes

Tree vs lightning rod: why does one burn and the other not?

The amount of heat generated by current flowing through a resistor (whether from lightning or more ordinary sources) is directly related to the power dissipated by the resistor, which is $$ P = I^2 R.$...
ACuriousMind's user avatar
  • 126k
38 votes

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 ...
badjohn's user avatar
  • 2,063
38 votes

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 ...
Hilmar's user avatar
  • 3,963

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