Questions tagged [electricity]

The study of the presence and flow of electric charge. Charges, currents, fields, potentials.

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80
votes
6answers
15k views

Why does public mains power use 50-60 Hz and 100-240 V?

Is there a physical reason behind the frequency and voltage in the mains electricity? I do not want to know why exactly a certain value was chosen; I am rather interested to know why that range/order ...
65
votes
5answers
140k views

Why do grapes in a microwave oven produce plasma?

Some of you may know this experiment (Grape + Microwave oven = Plasma video link): take a grape that you almost split in two parts, letting just a tiny piece of skin making a link between each half-...
59
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10answers
41k views

Why is the charge naming convention wrong?

I recently came to know about the Conventional Current vs. Electron Flow issue. Doing some search I found that the reason for this is that Benjamin Franklin made a mistake when naming positive and ...
56
votes
6answers
23k views

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

How can water be a medium to conduct current while its ionisation is so negligible that, in principle, no current should flow?
56
votes
6answers
6k views

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

For a few days, I was thinking of this question. Lets assume we have a simple circuit that is 100 meters long. And lets say that we have bulbs A, B and C connected to the circuit's 30th, 60th and ...
55
votes
6answers
82k views

Why do power lines buzz?

When near high tension power lines, particularly after a good rain, the lines themselves emit a buzzing noise. A similar noise can be heard coming out of the electric meters attached to my apartment. ...
54
votes
3answers
23k views

Why don't electric fish shock themselves?

Fish like electric eels and torpedoes have specially designed nerve cells that allow them to discharge hundreds of volts of electricity. Now, while pure water is usually nonconductive, the dissolved ...
51
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9answers
47k views

Does electricity flow on the surface of a wire or in the interior?

I was having a conversation with my father and father-in-law, both of whom are in electric related work, and we came to a point where none of us knew how to proceed. I was under the impression that ...
48
votes
7answers
16k views

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

Is it true that an electric current that flows through a conductor creates a magnetic field around the conductor? If yes, then why doesn't the magnetic sensor of my mobile device react in any way to ...
48
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3answers
17k views

Why do electric sparks appear blue/purple?

Electric sparks tend to appear blue or purple or white in color. Why?
45
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11answers
11k views

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

It is said that in a spaceship, you need to spend as much energy to brake as you spent for accelerating. An electric car, however, charges its batteries while braking, thus it actually recovers energy ...
44
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5answers
9k views

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

Problems The question I am about to make is either too stupid or hasn't bothered anyone because its obvious because I can't really find the answer anywhere. I am currently studying electricity and ...
43
votes
3answers
38k views

Why do we use AC for long distance transmission?

Why do we use AC (Alternating Current) for long distance transmission of electrical power? I know that AC is such a current that changes polarity (magnitude and direction) and has fixed poles.
43
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3answers
4k views

What causes electrical boxes to hum?

Often times you pass by an electrical box on an electrical pole and you hear a distinct hum emanating from it. What causes that tone? Does the flow of electricity itself have a sound? Or does the flow ...
42
votes
2answers
4k views

Wind generators - why so few blades?

Why commercial wind generators usually have just 2-3 blades? Having more blades would allow to increase power OR decrease diameter. Decreased diameter would also reduce stress due to different wind ...
40
votes
5answers
10k views

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

Household bulbs get alternating current, which means that the voltage of source and current in circuit keep changing with time, which implies that the power supply isn't constant. However, we don't ...
38
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6answers
223k views

Why is AC more “dangerous” than DC?

After going through several forums, I became more confused whether it is DC or AC that is more dangerous. In my text book, it is written that the peak value of AC is greater than that of DC, which is ...
37
votes
5answers
22k views

If the Earth is a good conductor of electricity, why don't people get electrocuted every time they touch the Earth?

Since the Earth is a good conductor of electricity, is it safe to assume that any charge that flows down to the Earth must be redistributed into the Earth in and along all directions? Does this also ...
37
votes
5answers
24k views

Speed of light vs speed of electricity

If I arranged an experiment where light raced electricity what would be the results? Let's say a red laser is fired at the same time a switch is closed that applies 110 volts to a 12 gauge loop of ...
37
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6answers
10k views

Does alternating current (AC) require a complete circuit?

This popular question about "whether an AC circuit with one end grounded to Earth and the other end grounded to Mars would work (ignoring resistance/inductance of the wire)" was recently asked on the ...
37
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1answer
2k views

Can lightning be used to solve NP-complete problems?

I'm a MS/BS computer science guy who is wondering about why lightning can't (or can?) be used to solve NP complete problems efficiently, but I don't understand the physics behind lightning, so I'm ...
33
votes
4answers
16k views

Birds sitting on electric wires: potential difference between the legs

We have seen birds sitting on uninsulated electric wires of high voltage transmission lines overhead without getting harmed, because sitting on only one wire doesn't complete any circuit. But what ...
32
votes
8answers
14k views

Since cables carry electricity moving at the speed of light, why aren't computer networks much faster?

Why can't cables used for computer networking transfer data really fast, say at the speed of light? I ask this because electricity travels at the speed of light. Take Ethernet cables for example, I ...
31
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5answers
18k views

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

When jumping a car battery the standard advice is to connect the red (positive) cable first. What's the physics explanation for this?
30
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4answers
15k views

I touched a tree that was touching an electric fence and got an electric shock. How is this possible if wood is an insulator?

I touched a tree that was touching an electric fence and got an electric shock. How was this possible if wood is an insulator? The tree wasn't wet either, and it was a pretty strong shock too.
29
votes
2answers
15k views

Static electricity and door handles

I have a pair of shoes, which seem to isolate me from the ground. In effect I'm gathering static charge and every time i grab an aluminum door handle, that current discharges and that hurts. Ouch. I ...
28
votes
6answers
8k views

Can a gym be built to supply electricity to homes? [closed]

A moving magnet induces a current in a conductor, then shouldn't we be able to generate electricity through manual labour? I was thinking about building a gym that used magnets as weights. People ...
28
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6answers
43k views

Lightning strikes the Ocean I'm swimming in - what happens?

I'm swimming in the ocean and there's a thunderstorm. Lightning bolts hit ships around me. Should I get out of the water?
28
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10answers
73k views

Electricity takes the path of least resistance?

Electricity takes the path of least resistance! Is this statement correct? If so, why is it the case? If there are two paths available, and one, for example, has a resistor, why would the current ...
27
votes
2answers
4k views

Please help identify this physics apparatus!

This was my grandfather’s and have no idea what it is only that it is some piece of physics equipment! The main black cylinder doesn’t seem like it wants to rotate but not sure if it should?
27
votes
1answer
11k views

Why do gases conduct at low pressure?

My intuition tells me if gases conduct electricity, it should happen at high pressure, then the atoms will be closer together and electric field can ionize them. But my textbook says low pressure is ...
27
votes
4answers
3k views

What causes the direction of lightning flashes?

During a lightning strike, the flashes appear as cloud to ground or cloud to cloud. Why is this the only manner of propagation? Why do the flashes not go upwards from the clouds into the sky?
26
votes
8answers
101k views

Difference between live and neutral wires

In domestic electrical circuits, there are 3 wires - live, earth and neutral. What is the difference between the live and neutral wires? As there is AC supply, it means that there are no fixed ...
25
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4answers
32k views

If air cannot conduct electricity, how can lightning happen?

If air cannot conduct electricity, how can lightning happen?
25
votes
1answer
4k views

Is it possible to overload a lightning rod?

A couple of weeks ago we had a big storm roll through the Chicago area. I watched as the city's skyscrapers were struck multiple times by lightning throughout the night and told my coworker about it ...
24
votes
7answers
5k views

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

I confuse the four kinds of fundamental interactions, so I think the electric force and magnetic force should not be classified as a big class called electromagnetism. Here is my evidence: The Gauss ...
24
votes
10answers
171k views

How to avoid getting shocked by static electricity?

sometimes I get "charged" and the next thing I touch something that conducts electricity such as a person, a car, a motal door, etc I get shocked by static electricity. I'm trying to avoid this so if ...
24
votes
3answers
8k views

Why do 'dead' batteries work again after exchanging the places of the batteries in an electronic device?

My camera, which is powered by two AA batteries in series, would not power on. I removed the batteries, exchanged their locations, and the device worked again - for another 15 minutes or so. The ...
23
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2answers
6k views

Can sugar be affected by a magnetic field?

While I was making a morning coffee at work, some sugar from the spoon started to fly away, seemingly towards some foam cups. Can this be explained by magnetism?
23
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2answers
16k views

How Special Relativity causes magnetism

So my physics teacher assigned us an article about how special relativity causes magnetism in a wire with a current, even with the low drift velocities of electrons in a current. It seemed that the ...
22
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3answers
83k views

How does load affect frequency on the power grid?

This story about the use of battery/freewheel based Frequency Regulators confused me about how the 60hz frequency of the North American power grid was set--saying that it was kept at that frequency by ...
22
votes
6answers
503 views

In aluminum, how does electricity travel through the surface oxide layer?

Suppose I connect a conductive wire (cross section 1 mm$^2$) to an aluminum object. Since aluminum is highly conductive, electricity will flow smoothly inside the object with little resistance. ...
22
votes
11answers
29k views

What is the difference between electric potential, potential difference (PD), voltage and electromotive force (EMF)?

This is a confused part ever since I started learning electricity. What is the difference between electric potential, potential difference (PD), voltage and electromotive force (EMF)? All of them have ...
22
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5answers
50k views

What are the fields produced around a current carrying conductor?

If you consider a current carrying conductor, every instant an electron enters the conductor, another electron will be leaving the conductor. Thus, the current carrying conductor will not be charged (...
20
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3answers
6k views

How is silver a better conductor than platinum?

Based on my understanding, platinum should be a better conductor than silver. Here's my reasoning and assumptions. An atom's ability to conduct is based on the amount of energy required to displace ...
20
votes
8answers
11k views

Why is capacitance defined as charge divided by voltage?

I understand that capacitance is the ability of a body to store an electrical charge and the formula is $C=\frac{Q}{V}$. What I don't understand, however, is why it is defined as coulomb per volt. Of ...
20
votes
3answers
785 views

Why can't batteries be charged quickly?

Charging of laptops, cell phones take so much time. Why can't we make such batteries easily/commercially which are charged more quickly? What's the thing behind this limiting?
19
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5answers
7k views

How many dimensions does electricity have? [closed]

My six year old daughter asked me this morning, 'how many dimensions does electricity have ?' What would be the best answer bearing in mind the age !?
19
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6answers
76k views

In an alternating current, do electrons flow from the source to the device?

If electrons in an alternating current periodically reverse their direction, do they really flow? Won't they always come back to the same position?
19
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4answers
6k views

Can a third type of electrical charge exist?

Upon reading my book on physics, it mentions that there are only two discovered types of electric charges. I wonder if there could be a third type of elusive charge, and what type of effects could it ...