# Tagged Questions

Electrostatics is concerned with the electrical fields and scalar potentials of stationary electrical charges and charge distributions. Use this for questions about electromagnetic situations in which currents and magnetic fields are absent, otherwise use [tag:electromagnetism] and/or [tag:magnetic-...

0answers
9 views

### Why x-axis E field exist in Electroosmosis Example

The explanation in Wiki said it is because the surface charge will induce electrical double layer at top and bottom surface, so that if we apply x direction E field, there will be a flow between two ...
2answers
82 views

### How can the fact that there is no electric field inside a hollow conductor be explained by Faraday's ice pail experiment?

Basically something very similar to these pictures These are from two separate books. The bottom picture says that all the excess charge in an object can be transferred to an already charged metal ...
2answers
43 views

### Calculation of electric potential in Geiger-Müller tube [closed]

We are given a cylindrical rod with linear charge density $λ$, and a coaxial cylinder with linear charge density $-λ$, as shown in the picture. We are to show that the potential difference between ...
1answer
36 views

### Capacitance of Nested Spheres

Imagine that we have two nested spheres and I wish to calculate the capacitance. First of all, I'm able to do the calculation. What I'm confused about is how it is possible for the Electric Field to ...
1answer
33 views

### What are the clicking sounds when static electricity occurs?

Sometimes, when there's static electricity, soft clicking sounds can be heard. This may happen when two fabrics are rubbed or when you get a static shock. What exactly causes this sounds?
2answers
58 views

### Induced charges

Consider a charge +q placed inside a cavity of conducting body. Charges will be induced as shown in the diagram below. How do we show that the electric field at a point A inside the cavity due to the ...
2answers
59 views

### Equipotential surface paradox

Consider a point charge +q as shown below. Now consider a equipotential surface and two points in it A and B. now the potential at A is equal to potential at B. If we now integrate (E.ds) from A to B ...
1answer
25 views

### Dipole-dipole field

Assuming that we have two parallel and exactly identical electric dipoles. How does bringing them together change their frequency? What would such field look like (how would they interact)? In fact, ...
2answers
180 views

### Why resistivity of copper wire is not zero even at zero kelvin?

At zero kelvin, everything seems dead stop. There is no movement occurring at zero kelvin, even at atomic level. As there is no movement in atoms, there is no vibration of atoms about their mean ...
3answers
49 views

### What is the field near a sphere of charge, with opposite charge inside?

This is a question from my high school physics class years ago. I'm embarrassed to say I still don't understand the answer. Say we have a non-conducting (like garnet) spherical shell, with -1 C ...
2answers
22 views

### Electric fields and potential

E = electric field V = electrostatic potential r = distance ' = derivative E = - (V)' therefore if E increases V decreases Also if r increases E decreases ...
2answers
83 views

### What does the movement of charge in an object mean?

When it is said that charge "moves" throughout an object, like if negative charge moves to the edge of an object and the charges become polarized, does this mean that the electrons has moved to the ...
0answers
164 views

### Non-parallel plate capacitor's capacitance [closed]

So far, I fully understood how to find the capacitance of a parallel plate capacitor. However, for the case of non-parallel plate one, how one could solve that kind of problem knowing that one plate ...
0answers
36 views

### Why is there a potential well near a hydrogen nucleus?

A hydrogen nucleus consists of a proton and the electric potential is given by the formula KQ/r where Q is +1.6×10^-19. So plotting a function of electric potential with distance r should give a ...
1answer
45 views

### No change in voltage in a capacitor

While trying to solve this question: Photo copy of the question and answer: Question:On charging a parallel plate capacitor to potential V the spacing between the plates is halved and a dielectric ...
1answer
27 views

### Gauss Law - charges outside the gaussian surface

I have just learned Gauss Law and this question is bothering me: Suppose a cubic gaussian surface and a charge next to its right side (image below). According to Gauss Law, the electric flux over ...
2answers
143 views

### How much is a Coulomb, really?

I've heard it said in my physics class that a Coulomb "is a lot of charge". And I believe it; most of the problems I've done in the class so far involve charges on the order of micro-Coulombs (or, ...
1answer
387 views

### How to draw equipotential surfaces for a dipole or system of two like charges?

How can we draw the equipotential surfaces (i.e the surface which has constant potential on all its points) for an electric dipole and a system of two like charges? I read it in some book that they ...
1answer
467 views

### Electric Field within the cavity of a conducting sphere?

So the hypothetical situation that I am confused about is below: The situation consists of a point charge, +q, contained within the cavity of a spherical conductor of neutral charge. I understand ...
0answers
13 views

### Method of image charges (hemisphere on metal) (2) [duplicate]

This is a continuation from Method of image charges (semisphere on a metal) . nbubis helped me a great deal concerning this problem and in this post I want to address my problem with the computation ...
0answers
20 views

### Method of image charges (semisphere on a metal) (2)

This is a continuation from Method of image charges (semisphere on a metal) . nbubis helped me a great deal concerning this problem and in this post I want to address my problem with the computation ...
2answers
103 views

### A capacitor with a conductor between the plates [closed]

Consider a parallel plate capacitor of area $A$ with a distance between the plates $d$, disconnected from the battery. I wonder, how would the capacitance of the system change if we placed a conductor ...
1answer
99 views

### Method of image charges (semisphere on a metal)

I'm currently trying to study ahead for the upcoming semester since I'm on break and I'm stuck on the method of image charges. I've tried watching some youtube videos on that topic and I thought I ...
2answers
749 views

### Graph for Coulomb force vs $1/r^2$

We know that when there is a relation like x inversely proportional to y^2, the graph would be like this: But in this question"Plot a graph showing variation of Coulomb force(F) versus $1/r^2$, ...
1answer
16 views

### Electric charge due to a point

In my book its written,"Electric field due to a point charge is inversely proportional to 1/r square....This means that at all points on the spherical surface drawn around the point charge, the ...
1answer
24 views

### Electric charges and fields

After solving a few questions i have observed two things...Are they true?: When two identical metallic spheres, one uncharged and one charged with lets say +4Q are brought close to each other then ...
2answers
2k views

### Perpetual motion machine [duplicate]

I'm having trouble understanding why this machine doesn't work. Part of a ring, half of which is uniformly charged, is located between two oppositely charged plates, attracting to the negative one and ...
1answer
52 views

### Doubt in derivation of electric field at axial snd equatorial point

Firstly, in derivation of electric field at an axial point due to a dipole we have to determine the Electric field at a point P on the axial. So there are two electric fields acting on this Point P, E(...
7answers
7k views

### Why doesn't an electron ever hit (and stick on) a proton?

Imagine there is a proton confined in a box and we put an electron at 10 cm distance: It gets an acceleration of thousands of meters/second^2 along a straight line joining the two CM's. One would ...
3answers
42 views

### How does a conductor shield the outside from its inside

If I have a charge of $+q$ placed arbitrarily within the spherical conducting shell, by Gauss' law, the E field produced will be created outside the shell, as if the charge were placed at the center. ...
0answers
83 views

### Electric field at centre of two different hemispheres

I have a sphere separated into two hemispheres which are insulated from each other the bottom half is earthed and the top half has potential $V$. Radius=$a$. I am trying to find the Electric ...
2answers
48 views

### How paper strips get electrified?

Why paper strips get electrified when we iron them? I have learned that when two insulators are rubbed then they gets electrified but in case of ironing a paper the iron is a conductor. Will rubbing a ...
1answer
31 views

### What is the location of point charge with respect to the original charged body?

we say if distance between two charged bodies is large as compared to its size then we take them as point charges and assume all its charge content to be concentrated at one point in space. What is ...
2answers
70 views

### Electric Potential from separating charges [closed]

Say there are 2 charges, one of charge C, and the other with a charge of -2C. C=1.5*10^-6 C. Initially, they are right next to each other. I pull them apart to a distance of 15 cm. So I can use the ...
2answers
62 views

### Can a system be designed that uses no energy to accelerate particles to high velocity?

I have one system in mind. Although I know it is not possible to accelerate a particle to a higher speed without spending energy, I would like to know why the proposed system won't work. The system ...
1answer
74 views

### What is the dielectric constant of a pure conductor?

Dielectric constant is the ratio of permittivity of a medium to the permittivity of free space. How to find dielectric constant of a conductor?
1answer
64 views

### Positions where the electric field is not defined

Can anybody help me to understand this statement given in my book? The electric field due to a discrete charge configuration is not defined at the locations of the discrete charges. For ...
1answer
25 views

### Charge in capacitor after switching voltage

Say you have a capacitor connected to a voltage source (vs). After the capacitor has fully charged, you cut the source voltage in half to vs/2. The voltage across the capacitor should change to match ...
1answer
53 views

### How to determine the cylindrical gaussian surfaces position while finding the electric field?

Today I encountered a question that had the solution: electric field outside of a charged nonconductor is $$E=\frac{\sigma}{2\epsilon_0}$$ which had the diagram below: Fig. 1 and for the ...
2answers
27 views

### Direction of motion of particle when placed on line of force

An electric line of force in the $x-y$ plane is given by equation $x^2+y^2=1$. A particle with unit positive charge, initially at rest at the point x=1,y=0 will move along the circular line of force. ...
1answer
94 views

### Four equally charged electrons are placed at the corners of a square. What charge should be placed in the center to keep them in place? [closed]

Here is a drawing: http://imgur.com/VdW1Xmv Trying to solve this question. I understand that the charge in the center needs to be positive, and the sum of all forces should be 0. But how do I ...
1answer
37 views

### Nonuniform charge distribution: total charge? [closed]

Can someone explain how the answer to part A is zero? All of my attempts at the question result in a non-zero answer.
1answer
65 views

### Electric field integration? [closed]

If we have a rod uniformly charged with $Q$ stretching from $-a$ to $a$ on the $x$-axis as shown in the picture And we want to calculate electric field in point $2a$ on the $x$-axis, we know that ...
1answer
29 views

### Electricity problem [closed]

• Two small metallic spheres, each of mass 5 g, are suspended as pendulums by light strings from a common point as shown in Figure. The spheres are given the same electric charge, and it is found ...
3answers
128 views

### Definition of equivalent capacitance

I know that equivalent capacitance of multiple capacitors in series is $$C = \left(\frac{1}{C_1} + \cdots + \frac{1}{C_n}\right)^{-1}$$ and in parallel is $$C = C_1 + \cdots + C_n.$$ But there are ...
2answers
46 views

### Do I need to use Pythagorean Theorem in 3d space for determining electric field induced by an infinite line of charge on a point?

An infinite line of charge with linear density λ1 = 8.4 μC/m is positioned along the axis of a thick insulating shell of inner radius a = 2.3 cm and outer radius b = 4.9 cm. The insulating shell ...
3answers
396 views

### How is Capacitance affected by a seperation distance and with or without a battery?

The questions specifically says this : A parallel-plate capacitor initially has capacitance $C$. The distance between the plates is then doubled, with a $9.0V$ battery connected. The battery is then ...
1answer
40 views

### Switching off Magnetic Field [closed]

A line charge (charge per unit length 'k') is put onto rim of wheel of radius 'R' which is then suspended horizontally, so that its free to rotate (spokes are made of non conducting material). In the ...
4answers
88 views

### Distance can be zero

Can a distance between two particles can be exactly zero? Example: If I have two opposite charged particles having uniform charge. They will attract each other and the distance between them will ...
2answers
82 views

### The separation between the two plates of a capacitor is increased

I had the following question on a quiz recently: A capacitor consisting of two parallel plates, separated by a distance $d$, is connected to a battery of EMF ε. What happens if the separation is ...