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

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42 views

Potential difference inside charge distributions

Always when I think about potential difference inside a symmetrical charge distribution, I think of it being equal to zero because it's dependent on the field and I imagine the directions of each of ...
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0answers
9 views

Is there any good book about the history of electricity? [on hold]

Is there any good book about the history of electricity? Electricity history starting from William Gilbert in the 17th century.
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1answer
20 views

Understanding electric field and potential inside an half-connected wire

Let's say we have a 9 V battery and a wire as shown in the image below: Let's assume H is the reference for measuring potential. I know the potential in F is 9 V, and I know the electric field in F ...
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1answer
26 views

Why did the electric potential energy fall in this situation?

Suppose you have two capacitors configured as shown in the image below. One of them has charge $q$ and the other one is uncharged. Then, you close the switch, allowing charges to flow. After ...
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2answers
37 views

Electric field on the surface of a charged sphere

We know that the electric field for a point charge is $$ E = \frac{KQ}{R^2}. $$ If $R$, i.e. distance from the electric field producer to the point where we want to find the electric field becomes ...
4
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1answer
38 views

Why does lightning generate multiple branches?

Everyone have seen how lightning occurs. But then I realized that lightning never occurs in straight lines but it follows branching. Why is that so ? Why can't lightning goes in straight line rather ...
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2answers
40 views

How can we prove that electric field originate from and terminate on charge using Gauss Law?

We already know that electric field originate and terminate on charge only and they doesn't make any closed path. But is it possible to prove this statement using Gauss Law ? If yes then how ?
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3answers
868 views

Why do lightning rods have a sharp point at the top?

We know that a lightning rod or lightning conductor is a metal rod or metallic object mounted on top of an elevated structure and, if we look closely, most of them have a sharp point at the top. What ...
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2answers
280 views

If we connect a block of p-type semiconductor only to a positive terminal, will it become positively charged?

Connect the positive terminal of a battery to a piece of p-doped semiconductor, say, silicon doped with boron. Will the terminal pull electrons out of the doped silicon, or equivalently, inject holes ...
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1answer
29 views

How do you calculate maximum current density for alternating currents?

I think the answer is neither here nor on Wikipedia but forgive me if it is, I don't read maths well. This question applies specifically to current density during transcranial stimulation with either ...
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1answer
26 views

single conducting plane and parallel conducting plane with opposite charge all have different Electric field but same Electric Flux?

Considering the electric field $\vec{E}$ created by an infinite conducting plane $M_1$ having surface charge density $\rho_s$ locate at xy plane at $z = 0$ with $\hat{a}_z$ as unit vector ...
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2answers
41 views

How is a potential difference created between two points?

I would like to know how potential difference is created between two points?Is potential difference created by adding more electrons at one side?If that's the case how to add more electrons at one ...
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1answer
347 views

How is the current flow perpendicular to the wire?

This answer gives a great explanation of how surface charge builds up to force the current to move perpendicular to the wire: http://physics.stackexchange.com/a/102936/41086 However, it fails to ...
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0answers
33 views

Why there is a difference in brightness of bulbs in series and parallel connection? [on hold]

Yesterday I connected two bulbs of 40 watt/220 v and 60 watt/220 v in both series and parallel connections. I noticed that when i connected the bulbs in parallel the bulb having low power i.e of 40 ...
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0answers
15 views

Do free charges in conductor in electrostatic field still moving even after the internal electric field is zero?

By the boundary condition, if an external electric field is apply to a conductor. The free charges of the conductor will move so that in the end There is no electric field or charge inside ...
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1answer
21 views

where does the term half in the formula of electrostatic potential energy comes from?(system of point charges)

Electrostatic potential energy stored in a system of point charges (from wikipedia) The electrostatic potential energy $U_E$ stored in a system of N charges q1, q2, ..., qN at positions r1, r2, ...
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0answers
22 views

Elementary problem on electrical charges [on hold]

The problem: On a small copper sphere there is an electrical charge $q=24 \mu C$. On another identical sphere, initially chargeless, is placed in contact with the first one e then brought to a $ r=40 ...
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4answers
1k views

How electrons move so fast in a electric circuit?

Whenever we switch on a bulb......it takes almost no time to glow up.....But we know that the atoms of a solid are tightly packed and there is a very little space between them. So how the electrons ...
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1answer
465 views

How can a fruit be used as a battery cell?

Fresh fruits can be used as batteries for glowing bulbs, but how this is possible? I mean how can electric charges flow through fruits? Do they contain chemicals like cells?
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3answers
507 views

number of electrons my laptop uses in a second

in order to confirm whether I understand the relation ship between amps, columbs and electrons I decided to try out the following. my laptop adapter's label reads 3.34 amps. I assume that: amps are ...
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1answer
39 views

How can equipotential planes differ in potential in an uniform field?

I'm trying to solve an exercise that asks me the field strength of an uniform electric field where equipotential planes differ by $1\ \mathrm{V}$ and are $2.5\ \mathrm{cm}$ apart. First of all, I ...
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2answers
21 views

Ohm's law holds at constant temperature - what about Joule heating?

Ohm's law states that the resistance of a conductor is constant provided its physical conditions, such as temperature, remain constant. But what I'm thinking is that as you increase the voltage across ...
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0answers
21 views

Current Electricity [closed]

Two cells of emf 1.5V and 2V and internal resistance 1Ω and 2Ω respectively are connected in parallel to pass a current in the same direction through an external resistance of 5Ω. calculate the ...
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1answer
32 views

What happens when a bird lands on a power line?

I know that when a bird is sitting on a high-voltage power line, virtually no current flows through the bird because there is (almost) no voltage drop between its legs, the two points are ...
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0answers
13 views

What is variable resistors? [closed]

What is the role of variable resistors in the electric circuit? Please give an example of electric circuit for variable resistors.
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2answers
29 views

Planet Sized Generator

I have an interesting idea for an energy generator and I want to see what you think. Basically, you take a small planet and drill from one side to the other so it looks like a sphere intersected ...
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5answers
129 views

The potentiality of the electric field

Could you please explain using just words why electric the field is potentially? I know the proof using integral: $$A = \int_{12}q\vec{E}\cdot{d}\vec{r} = qQ\int_{12}\frac{\vec{r}\cdot{d}\vec{r}}{r^3} ...
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1answer
52 views

Why can't I measure electric potential from source to point according to this formula

The formula for electric potential of points A and B in the presence of an electric field due to a point charge where $R_a$ and $R_b$ are the distances from source to point A and B respectively is: ...
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1answer
32 views

Is it possible to convert stored fat in the body into electrical energy directly? [closed]

Are there any research efforts to make a device to convert fatty acid into usable energy?
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1answer
33 views

Is there an electric field in the direction of a uniform current?

In an infinite plane where uniform current is passing through,is there any electric field? Because i know that charge produces an electric field but in a uniform current and because it is an infinite ...
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1answer
142 views

How do electrons distribute themselves along a wire attached to one pole of a battery?

Let's assume we have an electrochemical cell, like an AA battery. We attach a long straight wire to the negative terminus of the battery, the other end of the wire extends right away from the battery ...
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2answers
22 views

Calculating the energy supplied by a battery

If you wanted to calculate the energy supplied by a battery in time $t$ you would use $E=VIt$ where $I$ is the current through the battery. If the internal resistance is $r$ we could also use ...
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1answer
475 views

Non-conservative Electric Field

I was watching this video from Walter Lewin and while watching these two videos, I noticed there is a "contradiction" in what he is doing. All links direct you exactly to where he begins, so you don't ...
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0answers
28 views

Path independence of electric potential [closed]

I was asked to intuitively find the work necessary to move a particle from infinity to a point P perpendicular and near to a dipole's bisector through 3 different paths. Since one of those paths is at ...
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1answer
21 views

Experiment for finding resistivity

I was reading an experiment to measure the resistivity of a wire. I understand everything except for why the variable resistor is connected to the side of the positive terminal of the battery. Since ...
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1answer
24 views

Static electricity and insulators

I've read that Stephen Gray in his experiments on electricity, he has found that static electricity can be conducted -transferred- through an insulator thread made of silk. So, how could that happen ...
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1answer
34 views

Ampere's Law and Gauss's Law for EXACT CENTER of Finite Wire: Mathematical Justification [closed]

I have always seen it explained that: Ampere's Law (in integral form) works whenever B is constant around a path, so that you can pull it out of the integral. Similarly, if you can draw a ...
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2answers
48 views

Resistors in parallel: How do I make this rigorous? [closed]

In my revision guide it says "when two resistors are in parallel, the current has two paths it can flow through so there is less opposition to the current. This is why the combined resistance is less ...
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1answer
18 views

Question about ohmic conductors

I'm having some trouble understanding Ohm's law. My trouble is with the different ways it is described when referring to ohmic and non-ohmic conductors. If someone can answer this question I think it ...
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1answer
62 views

Filament lamp: Negative part of I/V characteristic?

I don't understand the negative part of the graph. It shows that the resistance is decreasing as the voltage goes from negative towards 0. What does a negative voltage mean and why does the graph ...
2
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2answers
37 views

How is resistance defined when there is no current?

By definition, a component has a resistance of $1\Omega$ if a potential difference of $1$V makes a current of $1$A flow through it. So I was a bit confused when I saw somewhere "a filament lamp has a ...
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1answer
17 views

Potential difference of conductor with induced load

If a metallic sphere is grounded and close to a positive charge q, it will be charged with -q. Let's say that the electrons will arrive through the grounding. This charge will cover the surface of the ...
2
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1answer
13 views

Need help understanding appliance ratings

I keep coming across things like "A filament lamp rated 12 V, 1.0 A", or "a heating element rated 230V, 500W". I think the first one is saying that a 12V potential difference across it will make a ...
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0answers
10 views

Circuit providing output? [migrated]

What does it mean for a circuit to provide an output power of say 1000W? Is "circuit providing power" referring to the battery supplying energy to the external circuit, or is it referring to the power ...
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1answer
15 views

Inductor in transformer

In an inductor, a current waveform 90 degrees out of phase with the voltage waveform creates a condition where power is alternately absorbed and returned to the circuit by the inductor. If the ...
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1answer
30 views

Difficulty understanding electricity concepts

In circuit diagrams what does it mean for energy to be used in going through a component? I usually see this when emf is being described: total energy supplied per coulomb by battery = total energy ...
-1
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5answers
47 views

Convert kinetic energy of a bullet into electricity and store it in a super-capacitor [closed]

I was thinking about bulletproof materials, they have to be so thick and heavy because they try to hold all of the kinetic energy of a bullet and then dissipate it (right?) So what if you made a thin ...
1
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1answer
36 views

The Faraday experiment about electric displacement field

I read the description and the explanation of the result of the experiment in my book but still I can't understand it. Here is the process of the experiment. A pair of concentric metallic spheres ...