All Questions
Tagged with electricity electrical-engineering
67
questions
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Why electric field increase near the cable connected in AC 220V socket even current is zero?
If I put low frequency electric field meter near the connected cable in AC 220V socket, he show 1200 V/m even if device is turn OFF(zero current), if disconnect cable from socket, field drop to 8 V/m.
...
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5
votes
2
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135
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What is the "closed circuit" of a bug swatter racket?
There are bug swatter racket that can kill fruit flies, mosquitos, or flies, if the insect touches the metal mesh.
However, when I look at the construction of the device, the metal mesh is all one ...
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2
votes
1
answer
185
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What can cause a spot above my WiFi router's antenna? [closed]
Lately a weird dark spot has appeared right above the antenna of my wifi router. It wasn't there before.
I have tried to wipe it and it got a little bit brighter but I don't think it's dust.
My guess ...
- 21
2
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96
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Why Faraday homopolar generator need brushes?
It is said that if one would attach a load physically to the rotating disc from center to rim no current would flow because both in the load wires and the disc itself currents would be generated in ...
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1
answer
104
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If a downed powerline contacts the metal chassis of my car, can I touch any metal parts of my car while sitting inside of it?
consider the following situation. I parked my car underneath some high-voltage lines – let’s say 380 kV-lines. Suddenly, one of the lines breaks in the middle due to a storm and one end of the (still ...
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1
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Current flow with no resistance
Imagine a simple circuit consisting of a battery with potential $V$ connected to a resistor with resistance $R$ by a loop of copper wire with $0$ resistance. It is obvious that a current $I=\frac VR$ ...
- 366
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2
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91
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What's the proportion of energy received on an overloaded generator?
I'm trying to understand the underlying physics with how generators work. I found this question which had some interesting answers, but it does not include all the details I'm after.
Suppose I have a ...
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1
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39
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If the rotational speed of a turbine at a power plant doubles, does its voltage, current or power double? [closed]
Somehow, I cannot find a simple answer to this question, or a simple equation or equations...
All other things being equal, if a turbine at your local power plant instantaneously doubles its rpm (or, ...
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9
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5
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4k
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Why is it easier to raise AC current to high voltage than DC?
In my country (and maybe all around the world I don't know) once electricity has been generated, it is then raised to 200k Volts for transportation.
I know this is to reduce the loss. Given $P=U.I$ ...
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433
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How do devices control how much power they use?
In power systems (Australian for reference) the grids run at a constant voltage of 220V. I’ve heard of switches were less voltage being used is created by adding more resistors for example to dim ...
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2
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3
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147
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Electricity supply in homes is AC but what about rms value that has only one direction? [closed]
In our homes, electricity supply is AC.but we have rms value in our homes...How do they relate? Is rms value generated in transformer or what??
- 21
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75
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Ramsauer–Townsend effect and Thermal Runaway in Thyratrons / (vacuum tubes)
A few years ago an EE told me that the Townsend effect was involved in thermal runaway within vacuum tubes. I can't seem to find any specifics on this on the internet. Can anyone disprove / verify and ...
- 23
2
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2
answers
47
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Why do the two relations of Power in a resistive load $P= I^2 R$ and $P = V^2/R$ (Assume Ideal resistances ) seem contradicting in this situation?
I have seen similar questions in the forum but they fail to be very specific .
I would ask the question from the viewpoint of Problem Solving. Let me put this question from a textbook :
A heater coil ...
- 27
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25
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Do you get correct graph of transfer characteristic, if you take +ive Vds(constant) value instead of -ive. As mostly CNTFETs are p-chnl FET
I'm studying transfer characteristic curve of CNTFET to get value for mobility, S.S, etc. According to my basic background knowledge, NMOS curves lie in the 1st quadrant. While for PMOS they lie in ...
- 11
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143
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What is causing the acceleration of charges in an ideal TEM transmission line?
As I understand, in an ideal TEM transmission line we can set up the telegrapher equations and solve to show that the line propagates voltage and current waves.
My confusion arises when we recognize ...
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2
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171
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What is the difference between horizontal units and horizontal scale at an oscilloscope?
This is a picture of the data of a given measurement by an oscilloscope. I would like to know what the difference between horizontal units and horizontal scale at an oscilloscope is. I would be so so ...
user277332
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1k
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Physical Meaning of Joule Integral
I have been reading literature on fuses and came across the joule integral or $i^2t$ value many times. Often, it is referred to as energy but I am confused because shouldn't energy be $E=RI^2t$? I ...
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1
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2k
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Will an appliance metal case get alive if touched by the neutral wire?
My phyiscs textbook only discusses what will happen if a live wire touches a metal case and how it turns alive, however, I was wondering, will the same effect happen to the metal case if touched by ...
- 377
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2
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526
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Physics vs Electronics (Smartphone charger)
Basically, an electric charger consists of a transformer, which transfers electrical energy from one inductance to another..
َAs i imagine the process physically the first circuit (inductance) should ...
- 67
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3
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739
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Why does the power remain constant during the stepping up and stepping down of current in transformers?
I understand quite a bit of transformers, their structure and other concepts and formulas related to mutual induction. However I'm not able to explain why the electrical power has to be constant ...
user248823
3
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1
answer
934
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in photoelectric effect, where do electrons go when they are ejected from metal?
When light shines on a metal, electrons are ejected from the surface of the metal provided the energy of the photons are greater than the work function of the metal.
My question is:
Where do the ...
- 147
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54
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How much energy do I need to charge an electric car? [closed]
Suppose I have an electric car with a battery capacity of N kWh, how many kWh of power do I need to recharge it? It can't be a precise match of N - some must be lost through heat, powering the ...
- 101
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1
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771
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How Equilibrium is Reached and Voltage Shared in a Series Circuit with Two Resistors [closed]
I've been reading up on basic electronics recently and to help me understand things better, I've been writing down my understanding of what I've read in layman's terms. One thing I've struggled with ...
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3
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200
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What device is universal for electrostatics?
In The varieties of material existence, Michael Nielsen says the following:
"It’s easy to design a programmable device which is universal for electrostatics in any given closed region of space. You ...
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1
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20
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Is it possible that two electric engines that has equal max rpm can work differently under load?
Two electric engines let's say has 3000 rpm with no load, but if I say they cope with work differently: one becoming weaker than the other under load or friction. Is it possible? If yes, why?
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661
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Why does this magnetic charger cause short circuit when it sticks to the metal leg of my table? [closed]
Recently, I have bought this product. It is basically a USB cable, with a magnetic end, and a tiny attachment that goes into the mobile device.
I plugged it into my laptop cooling stand (which has ...
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1
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315
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What causes changes in frequency in the Nation Grid electricity supply? [duplicate]
Following the power cuts in Britain this week, we were told that lack of power being generated led to a drop in the AC frequency as shown in this graph:
I understand why a stable frequency is ...
- 101
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74
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Modelling behaviour of a transformer
I'm looking for a physical-mathematical model to describe the behaviour or working point of a power transformer in dependency on its most critical parameters like oil temperature/heat dissipation, ...
- 1,507
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2
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54
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Current law explained
Kirchhoff's Current Law (KCL) is experimentally proven but what exactly happens?. I have made a model by taking the drude model and adding the interactions between the electrons and the reason why ...
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2
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1k
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How to calculate total power generated?
I have a circuit with a piezoelectric transducer which converts mechanical energy to electrical. The ceramic is connected to a 1 Megaohm resistor and a voltmeter which reads voltage.
If I want to ...
- 15
3
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1
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379
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Which types of collisions contribute to electrical resistivity?
Do electrons only bump with other electrons in a circuit and that only causes resistance? Or do they bump with the nucleus as well?
Here's a post I have been studying recently:
The path of a typical ...
- 165
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294
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What is the uncertainty on 50 Hz a.c.?
We are doing an experiment to measure velocity using the ticker-tape timer which runs on a 50 Hz a.c. 12 V power supply. I am in Ireland. So the time interval between each pair of dots is 0.02 s. But ...
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633
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Potential difference between two points
Okay so this might sound kinda stupid but I'm new to electrostatics and I was doing a question that asked me to find the potential difference between two points . Now I calculated the potential at the ...
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1
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Piezoelctric Ceramic Transducing Capabilties
Piezoelectric ceramics are able to work as transducers, outputting electrical energy when mechanical stress is inputted. However, most ceramics have high static voltage and low current and power ...
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1
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46
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How computer knows how much charged battery is? [closed]
How does phones and laptops knows how much charged the battery is? I found lot's of simple devices like tv remote can also do that. Whats the mechanism behind that and does it vary with different ...
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48
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Resonance curve of oscillating curcuit
I took a resonance curve (see below) for different (series) oscillating curcuits plotting I:f and found that the amplitude differs for different values of C and L. Why exactly is that?
Blue specs: $L=...
- 141
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3
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63
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Why is this a circuit in parallel if it is topologically different than a parallel circuit
I'm struggling to understand why the left circuit is equivalent to a parallel circuit. I'm trying every deformation in my mind I can think of but I can't seem to get out the second circuit.
Secondly,...
- 236
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1
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62
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How come the current is not determined only by the first resistor it encounters?
I was reading about circuits on this link, where they use a tollbooth analogy to explain electricity. Now either this is a bad analogy or I am missing something, but let's consider a circuit that ...
- 139
3
votes
2
answers
460
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Physics in the primary coil of an ideal transformer
My textbook says that when primary winding of an ideal transformer is connected to an alternating voltage, an alternating current flows which in turn produces an alternating flux which causes an EMF ...
- 295
3
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2
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197
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Apparent violation of energy conservation in an electromagnetic transformer system
First of all I would like to say I am not a native English speaker, so there might be some grammar mistakes. Sorry in advance for that!
I have been a whole month trying to understand what is going on ...
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2
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1
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65
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Does it cost more energy to turn on a CFL globe than it is to leave them on?
Say there is a 15 W CFL globe.
When turned on for an hour, it consumes electricity worth $10 in terms of energy consumption (made up cost for simplicity). If the occupants of the room periodically ...
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57
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3
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69k
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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.
- 703
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1
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Railway line conundrum [closed]
I found a wire joining those 2 cement slabs. I wonder what it does. Any ideas?
- 333
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3
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3k
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Why does a charged particle in a cyclotron moves in circular path?
Force on the particle is charge*(velocity×magnetic field intensity).
The magnetic field intensity is perpendicular to velocity of charged particle.
What is it that makes it move in a circular path?
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2
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2k
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Can an Oven being set to a different temperature cause electric board to go off?
Basically: the electrical system kept going off (when light goes down in a division due to too many electrical appliances on at a time, or their combined power consumption).
My roommate said it was ...
- 101
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2
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116
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When heat loss is more than energy generated [closed]
Suppose a electric power station produces 200W of electricity @ 200V. Now instead of stepping it up, it decides to transmit it as 200V to a city 20 km away. The transmission cable has resistance per ...
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0
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35
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Separating Interaction of Heat from Electricity?
I have a rod where electricity of frequencies 1-360 Hz is passed through. It is affected by heat. I am evaluating the energy involved in such a process, contributed by electricity and heat.
The ...
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1
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100
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Why current of a battery drops continuously in high currents?
I have asked this question on EE SE but could not get a satisfactory enough answer.
I have shorted an AA battery through an ammeter. Inititially, the current reading on ammeter was around 0.9 amperes ...
- 131
51
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8
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207k
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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 ...
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2
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2k
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Flow of charges in two different materials
Consider two cylindrical conductor rods: one copper rod and one aluminium rod. The rods contact at a circular face, aligned coaxially.
Their exterior circular faces are connected to some DC voltage. ...
- 31