# Tagged Questions

Electric field is defined as the electric force per unit charge.

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### Should the electric potential of a positively charged sphere be negative?

Because the indefinite integral of the electric field results in a negative value? (As the function is proportional to $r^{-2}$? I've got to be missing something... Help please!! Thanks! Also, I ...
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### Microscopic fields inside a conductor

In a neutral conductor if we assume electrons as point charges, the electric field in the space between them cannot be identically zero. This microscopic field may be very weak. What if we were very ...
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339 views

### Influence of charged particle's own electric field on itself

I read this in my textbook: A charged particle or object is not affected by its own electric field. Since I find this completely unintuitive and my mind is yelling "wrong! wrong! how could a particle ...
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618 views

### What do physical properties of materials trigger the capacitive touch screen?

I have watched some youtube videos about capacitive touch screen http://www.youtube.com/watch?v=ZHzaVzYEZbw http://www.youtube.com/watch?v=GmCE18RMEeQ The videos show that a conductor(finger), in ...
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332 views

### Electric field strength between 2 positive charges [closed]

I'm having a lot of trouble trying to solve this problem: Three identical point charges of magnitude $+1.0$ $mC$ are located at the corners of a square that is $1.0$ $m$ on a side. A point charge of ...
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994 views

### Gradient of the electric potential

I was wondering if for a point-like charged object, does the gradient of the electric potential point in the direction of maximum increase or maximum decrease of the function $V$?
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### Electric lines of force

Why cant electric lines of force pass through the charged sphere? Well, basically that's how a Faraday cage works, but how can it be so?
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### How does lightning “know” where to go?

If lightning comes down in, say, a large flat field with a lightning rod sticking out of the middle, the lightning will strike the rod. How does it "know" the rod is there? Will it always strike the ...
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254 views

### Explanation on the resulting forces of two positive point charges

Why will the resulting force lines of two positive point charges be like this: I would expect this:
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152 views

### Electric Field inside a hollow ball, excentred of a homogeneous charged ball

Q: We have a homogeneous charged ball with radius R which contains a ball-shaped hollow (with radius := r and distance from center of the bigger ball (M) to the center of the hollow (N) := b). ...
3answers
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### Why can we use Gauss' law to compute electric field?

For simplicity I'm considering only the sphere case. In the Gauss' Law formulation we have some field $E$ introduced by charges $Q$ inside some sphere, then we compute flux and integrate, and we get ...
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306 views

### Electric field caused by magnetic field

Does electric field caused by time varying magnetic field form closed loops(electric field starts from a positive charge and ends at a negative charge)? and are they conservative or non-conservative ...
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### Electric field singularity

What's a general proof for the log-singularity of electric field near the edge of a uniformly charged surface?
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457 views

### Finding the Electric Field (and other information, besides)

The problem I am working on is: Two parallel plates having charges of equal magnitude but opposite sign are separated by 29.0 cm. Each plate has a surface charge density of 33.0 nC/m2. A proton is ...
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### Electric field lines

If electric field lines cannot terminate in empty space, in the simple example of two equal charges what happens to the line starting from one of the charges toward the other in the middle?
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### Higher To Lower Electric Potential

The question I am working on is: "An electron moving parallel to the x axis has an initial speed of $4.65 \cdot 10^6~m/s$ at the origin. Its speed is reduced to $1.27 \cdot 10^5 ~m/s$ at the point ...
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300 views

### Finding the electric field

The charge per unit length on a long, straight filament is -91.9 µC/m. (a) Find the electric field 10.0 cm from the filament, where distances are measured perpendicular to the length of the ...
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### Electric force in DNA molecule

Given that distance between O-H and N-H bonds are 0.11 nm and How do I compute the net force exerted from Thymine and Adenine? A hint given is: Hint: To keep calculations fairly simple, yet ...
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248 views

### Revealing Electric field lines through Grass seeds in mineral oil

In one of Walter Lewin's famous lectures, he takes a small container almost completely filled with mineral oil and grass seeds (I'll keep looking for the video to link to it). He connects two ...
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838 views

### Electric field and insulator or dielectric

I have a uniform electric field $E$ projected from left to right and I placed an insulator or dielectric right in the middle of it. To the left of the insulator, the $E$ is the original $E$. Inside ...
6answers
291 views

### Relation between field strength and potential?

In terms of gravity and electric fields, I'm not sure what the difference is between field strength and potential is and how they are related? Both using maths and not.
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### The direction of electric field in a diode

Why electric field pointing to left? (The middle area is depletion region.) (This is without any external electrical voltage applied.)
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### How to draw electric fields correctly?

Draw a negatively charged plate A and a positively charged plate B with an equal charge. Draw the field. (the image is the given answer) I however do not understand why this is. Is there any reason ...
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### What forces affect point charges?

I am working on a point charge simulator, and I was wondering what forces can affect point charges (assuming that they operate in a closed system, with no externally generated light, and initial ...
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281 views

### Change in intensity of electric field with constant velocity

Consider a +Q charged particle is travelling towards another test charge +Q. Now what would be the difference in electric field experienced by the test charge(avoid the gradual decrease in distance ...
3answers
372 views

### Is there is any difference between Electric Flux ($\Psi$) and Total number of Electric Field lines ($E\times$Area)?

Is there is any difference between Electric Flux ($\Psi$) and Total number of Electric Field lines ($E\times$Area)? $\psi = \Sigma Q$, and $\phi$ = Electric field intensity $\times$ Area where Area ...
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294 views

### Intuition behind Fourier transformed spaces

Intuitively I've been able to understand a Fourier transform a change-of-basis formula - you're basically moving from position to momentum basis or from time to frequency - but what does it mean that ...
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### Working out the electron mobility from the transfer rate (1/s)

I have an electric field value for a uniform structure through which an electron travels. Given that I've calculated a transfer rate (frequency) for the electron when it goes from one molecule to the ...
2answers
80 views

### Production of electricity from atmosphere

I read the electric field intesity at the surface of earth is 100v/m. Then why can't we keep two metallic sheets at different heights and produce a continuous current by connecting these two sheets ...
1answer
769 views

### Electric field inside and outside a metallic hollow sphere

1) It is known that inside a metallic hollow sphere it will not experience outside electric field because of the charge separation of electrons and holes at the surface of sphere and creating an equal ...
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### Working out the electric field from applied energy

I have created a simulation of one electron bouncing through a 3D mesh of molecules. The electron hopping is determined by a calculation of electron transfer rate using the Marcus equation (a result ...
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410 views

### Finding the electric field for a shell of charge

Suppose we have charge density defined $$\rho(x,y,z) = \begin{cases} 0 & 0 \leq r < a \\ K & a \leq r\leq b\\ 0 & b< r \end{cases}$$ For some constants $K,a,b$ How would ...
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451 views

### Calculating the electric relative permittivity of fluid or medium?

I'm unsure of how to calculate the permittivity of a fluid. Permittivity differs from one fluid to another: $$\varepsilon=\varepsilon_r\varepsilon_0$$ Since it is an electrical property combined ...
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309 views

### Gauss Law for Electric Fields

What is the integral form for the Gauss Law for Electric Fields? or ?
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878 views

### The formula of the force exerted on an electric dipole by non-uniform electric field

When an electric dipole of moment $\mathbf{P}$ is located in a non-uniform electric field $\mathbf{E}$, there is an net force exerted on it. However, the formula of the force in some books is read ...
2answers
3k views

### Why is electric field zero inside a hollow metal sphere ?

The figure below shows a hollow metal sphere with a positive point charge $Q$ sitting outside it. What is the electric field at the center of sphere ? The answer is zero (look at here at the beginning ...
2answers
495 views

### electric potential at center of uniform electric field

it is said that the electric potential at the center of uniform electric field is zero. my question is that why is it zero? electric potential is the work done per unit charge. $V = W/q$ and this ...
3answers
238 views

### Energy stored in space/frequency electric field

I've come across a problem with finding the energy stored in time/frequency electric field. In space/time we have (taking $\epsilon = 1$)  Energy = \frac{1}{2} \int_V |\mathbf{E}(\mathbf{x},t)|^2 ...
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### Will the plates of a parallel plates capacitor keep its charge after being charged then seperated from the non- conductor?

If i had 3 plates 2 metals and 1 glass .I put them together to form a basic parallel plates capacitor. After charging it and approaching it to an electroscope nothing happened that's because ...
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2k views

### Electric field due to a solid sphere of charge

I have been trying to understand the last step of this derivation. Consider a sphere made up of charge $+q$. Let $R$ be the radius of the sphere and $O$, its center. A point $P$ lies inside the ...
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476 views

### Divergence of non conservative electric field

I'm looking for the proof that the 1st Maxwell equation is valid also on non conservative electric field. When we are talking about a electrostatic field, the equation is ok. We can apply the Gauss ...
3answers
282 views

### Compute closed line integral of electric field in circuit

I have a circuit where resistor is parallel to capacitor, which is charged with voltage U. How to compute line integral around closed loop to get the result of Kirchhof second law - ...
1answer
2k views

### Potential Gradient & Electric field…

Potential gradient is the negative of the electric field. Does the negative (here) means that its direction is opposite to electric field.? If it does mean this, How is the direction of the ...
2answers
301 views

### Electrostatic notion of voltage as it applies to circuits

I have a question that's been bothering me about electric fields, voltage, and circuit analysis. Initially, I came to understand voltage as it was taught in the context of electrostatics - through ...