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Questions tagged [electricity]

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

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Why does a surface charge experience electrostatic pressure from its own field?

In Griffiths he mentions that a surface charge experiences a force in the presence of an electric field, but then he specifies that a force experienced by the surface is one due to its own electric ...
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30 views

Current flow in dielectric liquid

For a dielectric liquid between 2 electrodes (e.g. r134a), how does current flow across the electrodes assuming there are no impurities and voltage is kept below breakdown. I think the fluid doesn't ...
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159 views

Why doesn't the electric potential constantly decrease in a circuit as the current moves from the positive to the negative terminal?

Why doesn't the electric potential constantly decrease in a circuit as the current moves from the positive to the negative terminal? Details and Assumptions: 1. The wires show no resistance.
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Charged particle and SHM [on hold]

A punctual charge +Q is fixed at the bottom of a vertical cylinder. Another particle of mass m and charge +q is placed in the cylinder above +Q, so its bound to move vertically without friction. Show ...
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Since water boils at room temperature in a near vacuum, is it possible to use this to generate electricity in some way?

This may be a blatantly obvious question but I've never heard about such a thing happening. Could this be possible in some way using a vacuum chamber to boil the water and spin a turbine?
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Electric Potential in the Center of a Electric Dipole

I thought the electric potential at point B would be positive because placing a positive charge at point B would cause it to move releasing energy while doing so. The answer key states that the ...
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3answers
2k views

Does A.C. make the material through which it is flowing vibrate?

So recently I have been studying A.C. circuits and the graphs show that the current oscillates itself as a function of time. Now, according to me an oscillating body vibrates. Hence, the oscillating ...
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2answers
26 views

Derivation of Magnetic Field from Infinite Wire

I'm trying to get my head around the derivation for the magnetic field of an infinite wire, in my notes I have the statement: Setup: Wire centred on the z axis, current has direction +z. "Biot-Savart:...
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In a circuit, the ammeter reads 5A and the voltmeter reads 20V [closed]

What will be the correct value of resistance? A) Exactly 4 ohm B) Greater than 4 ohm C) Less than 4 ohm
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Joule's heating effect

Can we derive joule heating effect or heating of current using energy conservation for electrons when current is varying with time ?Like using concept of drift velocity,potential diffrence across ...
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0answers
29 views

Total resistance of a light bulb with two parallel tungsten threads [on hold]

I'm currently studying for my exams, and am kind of stuck at this question. Please note that I am translating from Danish to English as well as I can, but there might be any mistakes. Feel free to ask ...
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1answer
30 views

How to calculate the frequency of an AC voltage given by $ e = 100\cos(\omega t) $

The standard equation of instantaneous voltage is :- $$ e = e_m \sin(\omega t) $$ In this case :- $$ e = 100 \cos(\omega t) \\ \implies e = 100 \sin(\omega t + \frac{\pi}{2}) $$ Now, $$ \omega = 2 \...
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atom Quantum electric electron [duplicate]

Hello can anyone tell me why we take Electric potential energy between oppositely charged particles negative. I know the formula but I need proper reasoning or its a convention . Actually I am taking ...
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1answer
11 views

Does charging any electrical device in exterme temparature affect the current flow?

Recently in an Electric vehicle(EV) charging station, the charging time to charge a particular vehicle was 1 Hour (18V capacity of battery), but now in temperatures beyond 40 Degree Celsius, it is ...
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1answer
124 views

Do the electrons arrive at the anode with some kinetic energy? Where does it go?

I'm studying electronics and circuits. I'm trying to understand how electrons behave as they move in a circuit, but there's something that still bothers me. Electrons have some potential energy (the ...
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17 views

AC frequency and Conductivity measurement

Hello I'm currently writing my Bachelor thesis and work with a probe which is supposed to measure the electrical conductance with an alternating current. Its composed of two electrodes made 5 mm long ...
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2answers
162 views

How does Lenz law conserve energy in this case?

A magnet is falling into the coil as shown. The current in the coil creates a magnet as shown ( by the right-hand grip rule ). Now, as the magnet falls towards the coil, the magnetic field strength in ...
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1answer
257 views

Confusion regarding Hall effect in semiconductors

In many places, it's mentioned that in hall effect, the holes move under the influence of magnetic field in the direction as shown in the figure. In this figure itself, the bound electrons move in the ...
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1answer
165 views

Electrical charge equilibrium and the piezoelectric effect

About the piezoelectric effect: if I press a crystal the electrical charges segregate and an electrical voltage appears on the other two faces of the crystal. See this link for example: http://www....
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1answer
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Glow discharge : Why is the voltage stable with increasing current in the normal glow mode?

In the characteristics shown, the normal glow mode is from F to G, the voltage is stable with increasing current. I understand the explanation of how the electrode current density stays constant(the ...
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1answer
3k views

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

My physics teacher brought this up in a lecture and I am not exactly sure what he is saying.
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5answers
2k views

Watts vs. volts amperes

What I understand: In simple DC circuits, this is a product of the current and voltage, such that 1 watt = 1 ampere x 1 volt I understand that a watt is a unit of power (change in energy per unit ...
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2answers
194 views

Water flow in salt solutions contemporary exposed to an electrical and constant magnetic field

When a permanent magnet is held motionless close to a salt solution which already has been exposed to an electrical field a flow in the water will be induced and can be detected by applying some ...
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1answer
122 views

Why don't we consider the electrical potential being converted into kinetic energy when working with circuits?

Assume we are working with a postive test charge : In an electrochemical cell work is done by the chemical reactions to move a positive test charge from the negative terminal to the positive ...
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2answers
38 views

Energy saving got natural world [closed]

If i send small amount of electricity (eg.10v) given input of circuit,can i using stepup transformer,now get 30v then it separate 10v to output,10v to input of circuit,10v using backup for inputer.i ...
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1answer
89 views

Why can't free electron flow in water to conduct electricity?

This question is related to how batteries work. In a battery, the electrons can only flow in conductors, because they can't flow in the solution. my own thoughts on the matter: I believe it is ...
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1answer
140 views

Are birds warming up on high voltage lines?

Birds are unharmed on high voltage lines, because they touch only one wire and don't experience voltage as the difference of potentials. However, birds also seem quite comfortable there. Could this be,...
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Is activation voltage the sum of voltage required to collapse depletion layer and band gap energy?

Is the energy released when an electron moves from the valence to conductance band states the activation voltage or is activation voltage the energy required for electrons to overcome the depletion ...
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1answer
45 views

How do electrons exit LEDs? Aren't they in the valence energy state?

If a conducting electron reduces to the valence band in an LED, where does it get the energy to go back to the conductance band upon leaving the diode so current can flow? I'm confused as to how ...
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3answers
3k views

Why does this capillary action generator not work?

So I was doing a bit of reading. Apparently the the obstacle to generating energy from the forces driving capillary action is breaking the surface tension at the top of a capillary tube. It is just ...
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1answer
32 views

Insulators and electric charges

I have two questions about insulators: Will the net charge on an insulator always be negative if it's rubbed? How can a negatively charged plastic rod transfer negative charges when it comes in ...
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1answer
36 views

Robert Boyle's discovery of electricity

I want to know what is the contribution of Robert Boyle in this discovery of electricity after Otto von gueriche?
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33 views

How does electric current continue to flow in a circuit despite there being zero potential difference?

Consider a conductor connected to a battery by conducting wires. When wires are connected then after a very small amount of time steady state is achieved and voltage across conductor becomes equal to ...
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2answers
128 views

Potential difference in a nonuniform electric field

Let's say I have two points in a nonuniform electric field and those points have the electric potential 10 V and 5 V. If I then would use a voltmeter to determine the voltage between those points ...
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1answer
125 views

General Question about Faraday Disk and a Loop

If we have a constant magnetic field, $B$, perpendicular to a rotating metal disk (essentially Faradays's disk), with some angular frequency, $f$ . Then there will be an emf across the ends of the ...
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1answer
69 views

Can electrons fly off a conductor?

This is probably a stupid question, but what if you made an electron flow through a superconductor so that the electrons build up speed flowing through the wire, and then cut the wire. Would the ...
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1answer
218 views

If we increase dimensions of a wire, how does electron density change?

If we increase the diameter of a wire, does the electron density change at all? When we increase the diameter or the length of a wire (while solving numericals) do we add appropriate number of ...
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2answers
23 views

What is it that drives the electrons from one plate to another through a battery in a capacitor?

The situation is as follows: You have a parallel plate capacitor, disconnected from a battery on both ends. We know the battery tries to maintain a constant potential difference between its two ends. ...
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21 views

Concentric cylinder cell constant

For a concentric cylinder cell (with liquid dielectric), mathematically the equation for the cell constant will always yield a lower value than for the parallel plate case for the same volume of fluid....
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1answer
139 views

Brightness of lamps

The brightness of the lamp (power) depends on two factors: The voltage and the current which flow through it. In Figure(A) as the variable reaistance increases its reaistance, the current which flow ...
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1answer
57 views

What forces are acting on electron in a circuit? Do electrons act on each other in a current?

What forces are acting on electron in a circuit? What is the source of such kind of forces? Do electrons act on each other in electric current? If i have an ordinary electric circuit with only one ...
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When mutual inductance is occurring between two coils, is self inductance always occurring in each individual coil?

When a coil connected to an AC generator creates an EMF in another nearby coil (mutual inductance), is self inductance simultaneously occurring in both coils?
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188 views

Why are some Air Gap Sparks Orange?

While testing the ignition system on my car with a variable gap spark tester I noticed that the spark was orange. I suspect that there may be a problem with the ignition coil such that there is ...
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0answers
5 views

when solar connected to grid , in solar invertor ac volatge increase with solar power increase? [closed]

at my site i have individual transformer of 16kva , and i connected 5kw solar on grid system. issue is that when we connect solar then in grid tie invertor ac voltage is increase and invertor triped ...
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1answer
252 views

Ohm's law and current due to magnetisation

I'm reading Landau's Electrodynamic of continuous media, specifically the following paragraph of section §29 (The magnetic field of a constant current): If a conductor carries a non-zero total ...
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1answer
55 views

Why does a voltaic cell induce an electric force proportional to voltage?

I'm trying to understand the intuition behind Ohm's law (that current is proportional to voltage). I understand the basics of the Drude model: if the electrons frequently collide and on average reset ...
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1answer
41 views

Electron gun design

I have a question about electron guns. I have read a lot, and all designs use high NEGATIVE voltage ($-1000$ V for example). Is possible to use high POSITIVE voltage like this drawing? Or do you think ...
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1answer
184 views

Spectrum of discharge of air

Where do the various colors in electrical discharge of air with a high voltage originate from? Are these transitions in ionized nitrogen gas or unionized gas? Are chemical reactions involved? I assume ...
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0answers
19 views

Cell constant and conductivity cell design [closed]

When comparing a concentric cylinder and parallel plate design for a liquid conductivity cell, which design is more favorable to get a smaller cell constant in a practical setting and why? (See below ...
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electric force of rubbing [duplicate]

When rubbing a ruler with my hair and get it closer to some pieces of papers , it'll attract them (they'll effect each other by an electric force). But why ? WhenI only charge the ruler not both of ...