Questions tagged [electricity]

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

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13 views

How much energy does it take to form a plasma channel with a laser?

The usage is for something like this https://en.wikipedia.org/wiki/Electrolaser I know that the laser is powered for an instant in which a plasma channel is formed for the electricity to flow through,...
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44 views

How do I calculate the capacity of a capacitor [on hold]

that is hooked on sinus voltage source $ V(t)= 100 \sqrt {2} sin(10^3t) $ $ V $ if the value of electric current $ I $ flowing thru the capacitor is $ 1 A $ ? do I transform $ V(t) $ to a phase form? ...
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37 views

Can a Peltier/Seebeck cell transfer energy from a “thermally insulated” system converting (a part of) thermal energy into electrical energy?

Suppose you have a closed system, as per the schema attached below, which walls are thermally insulated. Suppose you want to reduce the temperature of the fluid inside the closed system, without ...
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How much more should aerogel insulation increase total thermoelectric fridge efficiency? [on hold]

If the insulation of a mini fridge using Peltier devices which is usually something like polyurethane or a similar type would be replaced with Aerogel based insulation how much would the efficiency go ...
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1answer
39 views

Electric field in a circuit

The electric field is defined mathematically as a vector field that associates to each point in space the (electrostatic or Coulomb) force per unit of charge exerted on an infinitesimal positive test ...
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16 views

What is an electrified channel?

I've been asked to create a sketch of an electrified channel. I've never heard of this terminology before. I tried to Google it and it came up with either guitar related answers, or a few about ...
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33 views

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, ...
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17 views

Capacitance of insulated conductor with charge on insulation surface

I have an insulated wire at high voltage (10s of kV) running above a conducting ground plane. In my case, I expect that corona discharge will occur briefly after the HV generator is turned on, but ...
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29 views

In a circuit, do surface charges get influenced by external electric fields?

Hello ,This image represents surface charges in a circuit caused by the battery's electric field, if you were to place an other electric field source of the same magnitude (but not connecting it to ...
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61 views

Skin Effect Explanation

I do not understand some things about the Skin Effect. Its Wikipedia definition is: Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor ...
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38 views

Is the flow of charges in inductor though electric field zero?

How electric field inside the wire of an inductor is zero (i.e. material of which loop is made — note material is assumed to be a superconductor), then how electrons flow in an inductor if electric ...
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25 views

Electric field generated by disk and conductor

I'm trying to solve the following problem but I have some doubts. I have a disk of radius $R$ with charge $Q$ (positive) and, at distance $d$, an uncharged conductor (of radius $R$ as well). Both are ...
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Force on a current carrying loop

I recently encountered a question which went like this, A current-carrying loop is placed in a plane perpendicular to a long current carrying wire at a distance from it. What is the force acting on ...
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In a circuit having one resistor why do the electrons lose all their potential energy across that resistor and not do so if there are many resistors

In a simple circuit which consists of a battery and one resistor, why do electrons lose all their potential energy across this one resistor regardless of the magnitude of the voltage or the resistance?...
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65 views

If air is an insulator, how does an ungrounded electric generator move electrons?

Firstly, this is NOT a duplicate question. There have been similar questions asked, but no one has adequately explained this particular aspect of electric generators. Yes, they act as an electron "...
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1answer
60 views

What makes the internal resistance of a battery at microscopic level?

What makes the internal resistance of a battery at the microscopic level? And why does voltage drop when in a circuit compared to the open circuit voltage? I think that the field between the ...
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1answer
74 views

What is the theoretical maximum efficiency for LEDs?

Whatever efficiency you want to give in converting electricity to light. I'm guessing it would depend on the type of LED. I imagine limitations come from various reasons. It would be cool if there ...
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76 views

If you have an object pushing or pulling another object, can you convert that force into electricity without either object moving?

If you have an object pushing or pulling another object, is it possible to convert that force into electricity without either object moving? If so, what possible methods could be used for harvesting ...
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79 views

Does increasing the length of wire increase the work (energy) needed to move electrons from the negative terminal to the positive one?

Imagine a circuit which consists of a battery and a resistor with a certain wire length. Suppose that the batter supplies 9 Volts. I know that it is the electromotive force which pushes the electrons ...
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49 views

What happens to the excess electrons transferred to the door knob during static discharge?

If I have walked on a carpet with my shoes, and then go near the knob of a door, the excess electrons in my body get discharged to the knob. Are all the excess electrons transferred to the knob? ...
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66 views

What's the explanation of 'paper pieces and comb experiment' about static electricity on atomic level?

I know that the charged comb induces static electricity in the paper pieces.how does that happen? Do the atoms in the paper get ionized,the same what happens when the comb was rubbed on hair?please ...
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32 views

Benefits and Drawbacks of Swapping Associations of Positivity and Negativity of the Proton and Electron

For historical reasons, I understand that a proton's charge was assigned the label of "positive", the electron's charge was assigned the label of negative, and, crucially, equations of current in E &...
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91 views

Electrolyte and internal resistance

If you have a Daniell cell(zinc / copper), excess charges will build up on the electrodes making the open circuit voltage until the reactions halt. Now in normal situation when you connect their ...
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1answer
69 views

Coulomb's law experiment, why consider the distance between the body's centers?

In $F_e=\frac{1}{4\pi\epsilon_0}\frac{q_1q_2}{r^2}$, why did Coulomb consider the distance between the center of the charges? Why not the distance between the immediate outer surface between the two ...
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505 views

Power generation by extracting heat from the environment?

It is chilly outside now and I am kept warm by a heat pump with COP 5.5: eating only 0.6 kW, it steals 2.6 kW from the outside air (making it even colder) and delivers the resulting 3.2 kW into my ...
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Do surfaces charge distribution in a wire move?

Upon reading matter and interactions ,In the chapter "electric field in a circuit" and surface charge distributions in a steady current, The book dosen't explain why doesn't the surface charges move ...
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Are the plates of a battery really charged?

In a zinc/copper Daniell cell correct me if I am wrong : Zinc has 2 valence electrons. So it wants to get rid of them. To do so it sends them to the copper which needs 2 to complete its valence ...
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18 views

Does electric field vary with cross sectional area in a non uniform current carrying conductor?

Suoppose I have a non uniform conductor which is kept in a uniform electric field maintaining a constant potential difference across its ends.Both electric field and current density are a properties ...
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56 views

Confusion on negative charges, current, and direction

My text book seems to have two contradictory statements about the same subject. Under the electrical potential and capacitance chapter, it says that negative charges move from lower to higher ...
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40 views

Would a flow of current (of positrons) zap us?

I have read this question: Will Positron Cause flow of electricity? To your question, yes, positrons are just as good as electrons for carrying a charge. There is no difference between "...
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41 views

Why is it so that some of the paper pieces get stuck to it while others drop instantly when they stick?

When we rub a comb on our head and held it near pieces of paper then they get attracted because of induced opposite charge.
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85 views

Mathematical Model for a Pendulum in an Electric Field

I am studying Higher Level Physics and for my Physics IA I am doing an experiment determining the effect of the voltage between two parallel plates on the on the frequency of a pendulum in between the ...
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38 views

What happens if you connect a wire to the anode of a battery, but not the cathode?

My understanding is that the anode of a battery is positive while the cathode is negative. If you connect a wire between the cathode and the anode, then the electrons in the cathode want to flow to ...
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82 views

What makes air a good insulator?

What makes air a good insulator? My understanding of air is that its mostly just empty space with a few molecules whizzing around. Now consider a negatively charged ball suspended in air. Why don't ...
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1answer
55 views

Why is the Earth considered an infinite electron source or sink?

All the literature I've read says that Earth is pretty much an infinite electron source/sink. If you add or remove electrons from the earth, then the charge of the earth must change. Furthermore, the ...
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1answer
24 views

How to calculate the voltage of a DC motor?

I have a DC motor. But I don't know its voltage. If I connect with a 3.2V battery, then the motor rotates. Can I find the voltage of the motor from the rpm of the motor?
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65 views

Is Ohm's law valid for water?

I have $E$ (electric field intensity) in water. I want to find $J$ (current density). I don’t know if Ohm's law ($J=\sigma E$) is valid for water. If it is not valid, how do I may find out $J$?
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what Mass would be required to create measurable resistance in this circuit?

sorry I'm not a physicist or student in this is not homework I was just thinking about this. say you have a spherical Mass of a certain density I'm thinking say planet-sized and then tangent to the ...
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2answers
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How does a Leyden Jar work?

When electricity goes inside the Leyden jar, the inside of the jar is negatively charged. Then the aluminum foil on the outer layer of the jar is positively charged. Does the inside of the jar want to ...
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27 views

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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31 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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3answers
41 views

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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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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31 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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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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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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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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1answer
29 views

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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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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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.