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

learn more… | top users | synonyms

1
vote
1answer
81 views

Why does transformer winding need large numbers of turns?

In transformers there are large number of turns in winding for both primary and secondary sides around the core. So, my question is why can not we just put one or two turns in winding as we need to ...
0
votes
1answer
70 views

A confusion with solenoidal windings

I have seen in solenoids, toroids, transformers, electromagnets and machines that the core is pretty insulated. Over this the winding coil is wrapped but it is a bare coil (turns are not insulated to ...
5
votes
1answer
2k views

Does rubber insulate lightning more effectively than air?

Last week, an Ars Technica writer was struck by lightning. He says that the 911 operators were concerned about whether or not he was wearing shoes at the time, but he didn't think it would make much ...
0
votes
1answer
24 views

Difficulty understanding the energy transformations during resistance in a circuit

I am currently having problems understanding the energy transformations that occur when resistance in a solid conducting wire restricts current flow. From my understanding, resistance in a solid ...
1
vote
1answer
39 views

Transfer of electrons and static electricity

From what I currently understand about static electricity, electrons "jump" from one object to another, which object loses electrons depends on where it falls on the Triboelectric series. For example ...
3
votes
2answers
5k views

Why are electrons defined to have negative charge? [duplicate]

We normally think of the "default" or "root" state of things as being on the positive side of the spectrum. For example, we don't normally use a + symbol to ...
0
votes
0answers
16 views

Are the effects of faraday's law of induction worth considering in this experiment?

In my intro to physics lab at uni, we did an experiment where we were supposed to measure the amount of kinetic energy and momentum before and after collisions between two carts. For some reason, ...
0
votes
1answer
20 views

Short Circuit Fires

I understand that if there’s low resistance, Ohm’s law shows that the current drawn will be very high. However, isn’t resistance what causes heat in a wire? I get there’s a lot of current going ...
0
votes
3answers
32 views

Open Circuits vs. Charging a Capacator

When you attach a capacitor to a battery via two wires, charge transfer occurs from one of the plates to the other. However, in an open circuit, there is infinite resistance in the dead-ended wire, ...
0
votes
1answer
20 views

How many electrons pased in electrical circuit

Assume I have electrical circuit that is connected to 5V power supply and current straight is 1A. How to know how many electrons are passed in single point per hour?
0
votes
1answer
38 views

If I lick a 9V battery, why doesn't my tongue noticeably get hotter?

Power dissipated is I^2*R, I don't know the resistance of my tongue so I can't tell how much current goes through my tongue. A resistor I have does get hot and I'm guessing it has a higher resistance ...
0
votes
1answer
27 views

Power with varible resistance

I know that P=VI, but what i was thinking about is that if we kept the voltage constant and increased the resistance, we will have less energy consumed by the resistance per second. So, this seems ...
1
vote
1answer
9k views

What defines the brightness of a bulb?

So I have a question. There are three identical bulbs, 2 of them are connected in parallel and the third is basically in series, on the same circuit. If the one of the lamps in parallel breaks, what ...
31
votes
5answers
7k 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 ...
0
votes
1answer
10 views

Passive cathodic protection

Trying to understand what is happening when we need protect peace of Fe by placing on it more active metal (for example Zn) like ...
0
votes
3answers
51 views

Current and resistance

Why the current is the same at all of the positions in a series circuit??,although there are different voltages at different positions of the circuit. What i know is that as the electron passes one ...
3
votes
1answer
787 views

does a resistor slow down the flow of electrons or just let less electrons through? or is it both?

I like to have an intuitive grasp of whats happening our tutor said they 'resist' the flow of electrons but I want to understand exactly whats happening.
1
vote
0answers
25 views

The change of length of positive column in glow discharge

When I was doing the experiment of glow discharge, I lowered the voltage between electrodes and find that the length of positive column will increased quickly around a certain voltage(the interval of ...
1
vote
2answers
40 views

Shorting a Superconducting Coil with A/C

When a superconducting coil carrying a direct current is shorted, it continues to carry the current without loss (approximately), assuming it stays cooled and superconducting. What would happen if ...
1
vote
1answer
34 views

Did I calculate this voltage correctly?

I have just started to learn physics. Please forgive me if I am completely wrong or something, I have just turned 14 haha. I am trying to learn about how to work out voltage for my year 10 exams. ...
1
vote
0answers
28 views

If a heater was turned on its' own wire, would heating of the wire cause the resistance to increase, thus the current into the heater to decrease?

I'm thinking not, because; A) It wouldn't make much sense in the real world because you'd need to avoid ever turning a heater towards its own wire, and you'd have to regulate the temperatures of any ...
5
votes
1answer
199 views

Potential difference between Earth's surface and 2 meters above

Assuming Earth is a charged sphere of radius $R = 6400\times10^3$ m with uniform surface charge density $\sigma = -10^{-9}$ C/m2 and with $\epsilon_0 = 8.85\times10^{-12}$ F/m I find that ...
0
votes
2answers
22 views

Determine the size of a conductive medium

Are there any measurable characteristics that would allow one to discern the size of a conductive medium? Say I apply the same voltage to a two foot long wire and a four foot long wire. Is there ...
1
vote
1answer
44 views

Thevenin theorem

Hi i got the trouble and i miss the concept about v out in thevenin i have the circuit like this so i used voltage divider for finding the voltage at point 1, but how to finding voltage at Vo , ...
16
votes
5answers
74k 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 ...
0
votes
1answer
37 views

How soon would electrons start flowing once I closed a switch on a circuit that was one light minute away from the battery

In a circuit, how do electrons "know" when the circuit is closed? To my understanding, they do not start flowing unless the circuit is closed. How soon would they start flowing once I closed a ...
0
votes
1answer
43 views

Could someone simply explain how a railgun works?

Could someone simply explain how a railgun works? What could possibly accelerate an object that fast in such a short distance? I've heard it has to do with current between two rails, but I simply do ...
2
votes
0answers
63 views

Why does the characteristic curve (V vs I) for a light bulb backbend?

When teaching Ohm's Law, I have students do an exploration of a small, incandescent light bulb with a low frequency (1-2 Hz) sine wave. It's a simple series circuit of source and light bulb, ...
1
vote
0answers
15 views

Hollow metallic waveguides versus optical waveguides versus cables

In almost every physics program, you learn about electricity, electromagnetism, photonics, ... Within the electricity course, you learn about transporting electric energy as electrons through cables. ...
0
votes
0answers
24 views

What happens to the electrons at junction?

In a Closed circuit at any wire junction, one end of a wire is bound to an end of another wire . Now the Circuit is closed. So the electrons are passing through the wire. Now at the junction there is ...
0
votes
2answers
114 views

Is that ground, wall conductive?

If i put my foot exposed to ground and put my finger to the USB power, i will be electrocuted. So the electron(s) from the USB power is passing over my hand, run to foot and go to ground ? As i might ...
0
votes
3answers
72 views

Speed of electricity in cable [duplicate]

Movement speed of electricity in cable, is same as speed of light in space? In other words, electricity moves in usual electro cable aproximatelly 300 000 km/second ?
0
votes
3answers
64 views

Why does AC induction motor rotate the same way?

Suppose an aluminium disc is suspended where it can freely rotate. A magnet is placed above (not touching) the aluminium disc and made to spun. This obvious causes a changing magnetic field. By ...
0
votes
1answer
56 views

Why is the resistivity of a copper cable much higher than copper?

I was looking at the data sheet for a copper cable and noticed the conductor resistance to be specified at around 5 mOhm/m. This is magnitudes higher than pure copper, which has a resistance in the ...
0
votes
1answer
35 views

Why does not the electrons in a conducting the wire end?

What happens to the electrons in a conducting wire, Why does not the electrons in the wire end? I have read answers on the web but have not manage to understand, the free electrons from the ...
1
vote
1answer
32 views

Can we use a photon to use it as a changing field in an electric generator? [closed]

In an electric generator we use a changing magnetic field to create electricity. But what if we use a photon's oscillation of EM waves to generate electricity in a metal wire as we do in an electric ...
1
vote
0answers
22 views

Would it be possible to transform power using capacitors instead of coils?

Would it be possible to use capacitors to transform electrical tension (up or down), in the following way? Let's say you have a 10v battery, and you want to transform the tension up to 40 v. First, ...
5
votes
1answer
84 views

Does a Tesla coil work in space?

If I took a Tesla coil into space, and then turned it on near, but not touching metal objects- would charge jump to the metal objects? It's my understanding I wouldn't see a flash, since the lightning ...
4
votes
4answers
13k views

How can you have a negative voltage?

How can you have a negative voltage? I don't really understand the concept of negative voltage, how can it exist?
1
vote
2answers
7k views

Electron flow and electric potential

In the physics tutorial topic on current electricity it defines the positive terminal as the high potential terminal and the negative as the low potential. When talking about positive test charges ...
1
vote
1answer
67 views

Will a small magnet affect an insulated computer wire?

I'm designing something that involves a small magnet, probably about 0.5m in diameter, which will rest next to a computer wire carrying data, video, audio, etc. If the wire is insulated (think USB or ...
1
vote
0answers
37 views

Capacitors as Energy Wasting?

I am reading a lot of articles about capacitors as the energy storage. Let's consider simple circuitry which contain the battery and capacitor in series. The energy flow from the battery will be ...
1
vote
2answers
108 views

Does electricity have mass?

Given a superconducting magnetic coil, such as the ones at the LHC, is there a difference in the coil's mass when it is powered down versus when is powered up? Edit: This has been labelled a possible ...
0
votes
0answers
19 views

Electrostatic concept using for dust attraction

Can I use a charged electrode to attract dust particles from any surface? If yes, then surface should be conductve or non coductive? Or any other ways to do this by electrostatic concept.
0
votes
1answer
77 views

Question on Electromagnetic Induction

If a magnet is moving through a solenoid, why is there no electromotive force being induced while the magnet is at the centre of the solenoid? (Is it because emf is induced in both directions?) Can a ...
0
votes
1answer
25 views

How to configure two infrared light to produce two different intensity

I have two infrared illuminators that have the same properties (same wavelength, same number of leds, same angles, same max voltage and amperage). suppose that these illuminators are attached at the ...
3
votes
1answer
162 views

Is it possible to explain voltage and current using the wave nature of electrons?

Assume a battery and resistor are connected in a series. If we double the resistance, the current gets cut in half. This is a macroscopic effect. How do those electrons know that resistance has ...
1
vote
0answers
23 views

Electrostatics effect on resistance values [closed]

Consider two parallel metallic plates separated by a silicon dioxide layer of thickness tox (like a capacitor). In this case I am applying a positive voltage to the top metallic plate. Now due to ...
1
vote
3answers
5k views

How do I calculate the power consumed by a lightbulb?

I'm studying a lightbulb and its variable resistance, given by the expression: $R(T) = Ro[1 + α(T-T_0)]$, where $R_0$ is the resistance of the lamp at $T_0$. In this case, $R$ is not given by Ohm's ...
1
vote
5answers
2k views

Resistance between two points on a conducting surface

Suppose we have a cylindrical resistor, with resistance given by $R=\rho\cdot l/(\pi r^2)$ Let $d$ be the distance between two points in the interior of the resistor and let $r\gg d\gg l$. Ie. it is ...