Questions tagged [electricity]

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

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Resulting electric field when neutral conductor is placed in a uniform field

Start with a uniform electric field. Then, place a neutral, solid, spherical conductor somewhere in the field. The electrons will move to the surface and rearrange themselves until the electric ...
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3answers
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Charge on hollow spherical surface

Let a point charge $+Q$ is placed in center of hollow spherical conductor of inner radius $a$ and outer surface $b$. Then the charge on the inner surface of radius $a$ is $-Q$ and outermost surface ...
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A typical question of electric field [closed]

Two wires AB & CD, each of length 1m, carry a total charge of 0.2 microcoulomb each and are placed as shown in figure. The ends B & C are separated 1 m distance. Determine the value of ...
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Electrify a refrigerant

I am HVAC student and was contemplating a way to increase heat exchanger efficiencies. Examining a copper-coil exchanger, I wondered whether the number of coils might affect heat transfer, controlled ...
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2answers
54 views

Confusion regarding drift velocity

We define drift speed of an electron as the average speed of the electron inside the conductor, which is the distance travelled by the electron between two collisions divided by the average collision ...
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2k views

Why isn't current carried through a vacuum?

The empty vacuum of space shouldn't offer any resistance to a travelling electron, and so a large collection of electrons should similarly travel through a vacuum without resistance. As a result, the ...
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56 views

Inducing electricity

I'm trying to under stand electromagnetic induction more and have been looking up all the ways to induce a coil with a magnet and keep only finding these three types of examples. I’m confused as to ...
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Potential difference across a resistor in a simple circuit

In a physics worksheet that I have, I stumbled upon a simple circuit with a battery (with it's own internal resistance), a voltmeter parallel to the battery, and a variable resistor parallel to the ...
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1answer
31 views

How do electrons actually move in an alternating current?

Here's what I think the motion of electrons would be like. Let's say the electrons were initially at rest. Now, when the voltage starts increasing, the electrons start accelerating faster till the ...
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2answers
30 views

Convention for expressing voltage between two points

Voltage is always related to two points, because it means a difference in electric potential, between two points. If we want to express the voltage between A and B, we could say: The potential at ...
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1answer
20 views

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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Why is there an “electric” potential drop across the resistor?

An electric potential difference is created when two charges are separated. In a capacitor, there is a clear accumulation of opposite charges on the two separated plates, therefore work has to be done ...
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Dielectric Slab: Force due to fringing field

A parallel plate capacitor whose plates are maintained at a constant potential difference has a partially inserted dielectric slab. The force on the dielectric slab is given in most of the books. (...
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Could approaching an unknown object in space electrocute you? [closed]

Say you're out for a spacewalk on the ISS one day, and you see an unknown object floating next to you (ignoring the probability that it somehow matched your orbit perfectly and didn't just plunge ...
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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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2answers
74 views

Faraday's Law and Electromagnetic Induction

Faraday's Law of electromagnetic induction states that the rate of change of magnetic flux linkage is proportional to the $\mathcal{emf}$ induced. For a conductor, the formula goes $$\mathcal{emf}=N\...
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Why do I often get electric shocks from escalators and how to avoid this?

When I wear at least one cotton clothe and using escalators in different buildings containing escalators, I often get electrical currents in first touch of the relevant escalator, but right afterwards ...
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Relation between current and frequency

I look at a charged wire that is formed like a circle. I let it rotate with a frequency $f$. Which law gives me the relation between the charge of the wire, the rotation frequency and the current? I ...
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1answer
109 views

Why do diodes block current in a single direction?

It seems like all the explanations for diode mechanics simply state that if N-type semiconductor is connected to V+ of the battery, the depletion region grows so current cannot pass. It seems, ...
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Nickel plated steel strip for li-ion Battery pack - Purpose of Nickel Plating?

I am trying to build a battery pack from 18650 batteries, each interconnection is made from steel strip, most '18650 strip' has a steel core with nickel plating. I have a question regarding the ...
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1answer
144 views

Surface resistance calculation for non-rectangle surface

I have thin film on dielectric with equal surface resistance trapeze and when applying voltage (at grey area) hot area appears. How to calculate resistance field for trapeze to eliminate hot spots and ...
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1answer
38 views

How is it possible to get electric shock upon touching rails of an escalator?

I was wearing a pair of well insulated/thick-soled shoes, when I touched the rails of an escalator (which was wrapped/covered with probably insulating material which looked like a glossy rubber) and ...
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3answers
40 views

Why does the voltage drop in a cell increase if a heavy current is drawn from a cell?

"If a heavy current in drawn from a cell, a large number of charge carriers flow through the electrolyte sand hence more work is done. This results in more voltage drop, so terminal voltage decreases"-...
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creating a varying electric field across a copper strip

Hi I am trying to create a varying electric field (by position on copper strip) across a copper strip by attempting a standing wave pattern. the following is a diagram may I have some guidance on how ...
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Why does an increase in terminal voltage cause current to decrease?

This is part of a lab report that I'm writing and I don't really know why an increase in terminal voltage would cause a decrease in current. I have derived this mathematically, and through the data I'...
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1answer
57 views

Why aren't salt water batteries used to power cars instead of lithium-ion?

I know salt water batteries are less efficient than lithium-ion, but water is safer, can be found anywhere, is cheap and 100% ecological. Even if it doesn't last long, you can refill anywhere. Why can'...
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How does a gas discharge tube work?

How do cathode rays cause the electrons in atoms to jump up energy levels (since this has to happen so it can go back down an energy level and release light right)? Does an electron just bump one of ...
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Time it takes a coin to fall in a magnetic field

This was a homework problem of mine was: "A coin is placed on its edge in a vertical magnetic field of $B=20$ T. The initial angle between the coin and vertical is $\theta_0=0.1$ rad. Estimate how ...
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22 views

A question on Ampere Circuital Law

If we consider an infinitely long wire carrying current and apply the law by considering a circular loop at a distance $r$ we get, $$B=\frac{\mu i}{2r\pi}$$ All good. But If I apply the same law for ...
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1answer
28 views

Floating Voltage Referenced to Ground [closed]

So, I came across something interesting today at work that is completely confusing me. We have floating 130V battery backups, and I am told there is neither any ground reference, nor any center tap on ...
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66 views

How does time dilation affect power transmission (and V, A, W, Hz)?

How is the generation and consumption of electricity affected under the influence of time dilation? (For instance, a colony ship under the influence of a black hole) To get some hard numbers into ...
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Materials Electrical resistance and conductance

These images are right if the material is good conductor. But if this object is made by resistive material, two plates are made by resistive material, Can it possible ?
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DC Motor: Split rings vs commutator [closed]

Question: In a simple DC motor (as shown below), explain the effect that replacing the commutator with slip rings would have on the operation of the motor, if no other change was made? My Attempt: I ...
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5answers
580 views

Faraday Cage Explain (Gauss Law)

I was given the following explanation of Faraday cage: There is no electric field inside a hollow, charged conducting shell because a Gaussian surface inside the shell must have zero flux through it ...
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Salt water and electricity

It's well known that if you place 2 electrodes connected to a battery in salt water, Positive ions will get attracted to the negative electrode, and negative ions to the positive electrode. But what ...
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31 views

Capacitors and voltage rating

Imagine a battery that creates a +9000V Potential difference in respect to ground (The Earth) in it's positive terminal. (The Earth is at 0V in this example) And a +8992V potential difference in ...
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3answers
88 views

Is it true that whatever current enters a battery, also leaves the battery? Why?

How is it true that whatever current enters a battery also leaves the battery? Is it due to one of the Kirchhoff's laws? Can anyone show how that is? How can I reach this conclusion logically/...
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Is a 40 V/m electric field, coming from a wall socket and measured in air, a safety hazard? [closed]

I used a gaussmeter close to my child’s crib. Her head faces about 1 foot away from an electric socket. I was surprised it measured about 40 V/m at the socket and then gradually went down but was ...
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42 views

Relationship between current and voltage (I know little physics)

I'm a little confused about the relationship between voltage, current and resistance. I do know V=IR; but as to the relationship between voltage and current- (holding resistance to be constant) does a ...
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1answer
12 views

Different electric fields

What is the difference between an $electrostatic$ and a $non-electrostatic$ electric field?
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Can We Create Artificial Clouds In A Controlled Environment For Studying?

I would like to know how clouds produce electricity. So, in order to do that, we must closely study clouds. If we can create artificial clouds in a controlled environment, it will shed us some light ...
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1answer
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Does Low Temperature Attract Negatively Charged Particles?

I'm studying the effects of temperature in producing electricity like in clouds that produces lightning. Since dark clouds during a thunderstorm is below freezing point, it attracts negatively charged ...
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Calculating the stress tensor for a toroid with rectangular cross-section

I'm trying to calculate the Maxwell Stress Tensor $T_{ij}$ for a toroid with rectangular cross-section (height h, inner radius a, outer radius b). From Biot-Savart Law we can calculate the magnetic ...
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2answers
33 views

Potential drop in a wire having negligible resistance [duplicate]

What causes a potential drop in a resistor or load? Why a wire having neglible resistance have same potential across it? The given figure is of a stretched wire potentiometer. My question is why ...
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3answers
3k views

What is the physical explanation for energy transport in simple electrical circuits?

Keeping it simple, what is the physics approach to a current in a wire connected to a battery? How does the electric field behave? I've read somewhere that, contrary to the common conception, ...
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1answer
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Confusion about the relationship between current, resistance and potential difference

If the voltage of a component has dropped, what will happen to the resistance? My book says it will decrease but I don't understand the logic. How can current and resistance go down at the same time? ...
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Faraday Ring: original drawing and description?

Does anyone know where this is locateed? I’ve been having a challenging time finding the original drawing with description text And experiment description. I have found a picture of the ring, ...
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1answer
81 views

Salt and electricity

Recently, I did an experiment with salt and electric current. I set up an open electric current in a used battery holder where the missing part of the circuit is two metal plates. I then fill this ...
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1answer
32 views

Forces Acting On a Bar of Magnet Inside a Solenoid

If you have a solenoid placed like this: and you drop a magnet inside the coil will the change in acceleration of the bar of magnet inside the solenoid coil over change in time be 0? i.e. will the ...
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1answer
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Does potential difference depend on the size of an object

Let's say object A has received a number x of electrons and is now at a 1v higher potential relative to a neutral ground. Now if object B which is 2 times bigger than object A receives the same ...