# What is Charges: Definition and 1000 Discussions

Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. There are two types of electric charge: positive and negative (commonly carried by protons and electrons respectively). Like charges repel each other and unlike charges attract each other. An object with an absence of net charge is referred to as neutral. Early knowledge of how charged substances interact is now called classical electrodynamics, and is still accurate for problems that do not require consideration of quantum effects.
Electric charge is a conserved property; the net charge of an isolated system, the amount of positive charge minus the amount of negative charge, cannot change. Electric charge is carried by subatomic particles. In ordinary matter, negative charge is carried by electrons, and positive charge is carried by the protons in the nuclei of atoms. If there are more electrons than protons in a piece of matter, it will have a negative charge, if there are fewer it will have a positive charge, and if there are equal numbers it will be neutral. Charge is quantized; it comes in integer multiples of individual small units called the elementary charge, e, about 1.602×10−19 coulombs, which is the smallest charge which can exist freely (particles called quarks have smaller charges, multiples of 1/3e, but they are only found in combination, and always combine to form particles with integer charge). The proton has a charge of +e, and the electron has a charge of −e.
Electric charges produce electric fields. A moving charge also produces a magnetic field. The interaction of electric charges with an electromagnetic field (combination of electric and magnetic fields) is the source of the electromagnetic (or Lorentz) force, which is one of the four fundamental forces in physics. The study of photon-mediated interactions among charged particles is called quantum electrodynamics.The SI derived unit of electric charge is the coulomb (C) named after French physicist Charles-Augustin de Coulomb. In electrical engineering it is also common to use the ampere-hour (Ah). In physics and chemistry it is common to use the elementary charge (e as a unit). Chemistry also uses the Faraday constant as the charge on a mole of electrons. The lowercase symbol q often denotes charge.

View More On Wikipedia.org
1. ### How do we know the point of 0 electric field is on the axis?

In many homework problems I've encountered, they all seem to assume the electric field = 0 point is along the axis of the two charges. Intuitively it kind of makes sense, but I'm looking for a solid justification for it. In other words, why can't it be off the axis of the two charges? When...
2. ### Electric Field of two charges

I have attached an image of what *I think* the electric field looks like. Would this be correct? I am convinced about everything here, apart from the ones on the far right. All the other ones loop from the +ve charge to the -ve charge, but where do the grey lines on the right loop to (the ones...
3. ### Looking for practice problems for "Method of Images" for charges

Homework Statement: I am looking for practice problems for "Method of images of charges" Please help Relevant Equations: b=R^2/a q2=-R/aq1 I am preparing for IIT JAM
4. ### Potential of Charges on a Grid

Looking at the image, I see that due to symmetry, the bottom-left negative charge and the bottom-right positive charge cancel out, leaving me with a triangle around the center. I'm not entirely sure how to solve for potential at the origin specifically, but I believe that the potential energy of...
5. ### Find the magnitude of the electric force from 3 charges at vertices of a cube

There are three charges with +1 μC and −1 μC, are placed at the opposite corners of a cube with edges of length 1 cm, and the distance from P to B is 1cm 2. I labeled them as A, P, and B, which is shown in the diagram below. Since we need to find the magnitude of the charge at point P and the...
6. ### Multipole expansions, calculating the various moments of point charges

Problem: Solution: This was quite simple, are my solutions correct?

8. ### Surface density of the charges induced on the bases of the cylinder

The correct answer to this problem is: ##\sigma = \varepsilon_0E\frac{\varepsilon-1}{\varepsilon}## Here is my attempt to solve it, please tell me what is my mistake? ##E_{in} = E_{out} - E_{ind}## ##E_{ind} = E_{out} - E_{in}## ##E_{in} = \frac{E_{out}}{\varepsilon}## ##E_{ind} = E_{out} -...
9. ### Force between point charges at the center of two spherical shells

If these point charges were placed in vacuum without any spherical shells in the picture, then the force between these charges would be ##F =\dfrac { k q_1 q_2} {d^2}##. But, I am unable to reason how spherical shells would alter the force between them. I do know that if charges were on the...
10. ### Graphing electric potential for two positive charges

For part (a) of this problem, The solution is However, my solution is Am I correct? In the solutions that don't appear to plot the electric potential as units of ## \frac {k_eQ} {a} ## like I have which the problem statement said to do. Many thanks!
11. ### Force between 2 point charges in VECTOR format (x i + y j + z k)

I tried using the distance between r2 and r1 and plugging them into the equation for i, j, k. >> So for the force in the x direction it was k*(4E-6*4E-6)/(4-9)^2. The answer I got was wrong according to webassign. Can someone please tell me what I am missing?
12. ### Electric field due to n charges

For this problem, The solution is, However, should they be a vertical component of the electric field for the expression circled in red? I do understand that assuming that when the nth charge is added it is placed equal distant for the other charges so that a component of the electric field...
13. ### Electric field due to two charges

The problem and solution is, However, I would like to know why it cannot be solved like this: Thanks for any help!
14. ### Resources on Simulating Charges in Magnetic Fields

Hey all. I started messing around with making a simulation involving charged particles moving in magnetic and electric fields and I was wondering if anyone had any good resources on the subject. I should be fine on equations, as I already have a book that should have everything I need about the...
15. ### Electromagnetic linear momentum for a system of two moving charges

When you write out the equations of motion for a system of two isolated charges, you can add both of the equations and get the increase in the particles linear momentum on one side. On the other side, you get the sum of all the forces between the particles. I understand that this sum of forces...
16. ### I Question regarding how to interpret dipole moment for bound charges

How do I interpret physically what dipole moment is ? The explanations that I received were "two charges seperated by a small distance " ,"it talks about ability of a dipole to rotate under the influence of an Electric Field " ,"Second term of the Multipole expansion" ,I get that these terms...
17. ### Coulomb's law — A negative charge balanced between 3 positive charges

hello i would like to understand something, i found the right answer but there is still something i don't understand. here is the figure and here is my correct solution what i don't understand is why F(3,Q) is 3kQ/r^2 i mean why is the 3? i only calculat the force between q3 and Q so why...
18. ### I Question regarding Laplace's Equation for regions with charges

Why doesn't the **Laplace's equation**(#\nabla^2V=0#) hold in the region within the sphere when there is a charge inside it ? Is it because #ρ \ne 0# within the sphere and it becomes a **poisson equation**($\nabla^2V=\dfrac{-ρ}{ε_0}$) and changes the characteristics of **Harmonic Solution**...
19. ### I Superconductors and moving/accelerating charges

How do one get the electrons to move inside a superconductor? Since I have understood superconductors repel magnetic fields due to the Meissner effect, or is that when the charges already are moving within the superconductor? If so how did we get them o move from the beginning? Can you make...
20. ### Limits of Partial Charges in Dipoles

In my book it is written "Ends of dipole possesses partial charges. Partial charges are always less than the unit electronic charge (1.6×10−19 C)". Suppose in a double bond(two electron is shared by each atom) or triple bond(three electrons are shared by each atom), can the electronegative atom...
21. ### I Does the property "equal charges repel" still work for non abelian theories?

I recall that there was an argument from Born expansion showing that exchange of odd spin between equal sign charges generates a repulsive potential, and if the charges are different or the spin is even the potential is attractive. I wonder, how does it work for non abelian gauge theory...
22. ### Electric field strength at a point due to 3 charges

I got E. 13q as the answer. That is what i did: The electric field due to +q at origin 0 should equal the electric fields of charges -3q and the new charge placed at 2x. So applying the equation above like this; k*(q) / (2^2) = -3q*k + (k*C)/ 4 solving for C the new charge added, gives 13q. I...
23. ### Seeking Guidance to Find Surface & Volume Bound Charges of a Half Cone

This was a trivial question I had (which I posted here on the PF EM Forum: https://www.physicsforums.com/threads/bound-charges-polarisation-of-a-half-cone.1015308/). As I received no response on the above link I decided to post the same as a self formulated HW problem. Below I have attached an...
24. ### Calculating the point where potential V = 0 (due to 2 charges)

Apparently, there are two solutions where the electric potential is zero which I don't understand, can I get some input on how this is possible? I have one thing in mind (which I just thought of and might solve it), the equipotentiality i.e. when I draw a circle for V = 0 around the negative...
25. ### I If we take two charges and hold one still, what are the forces?

If we take two positive charges +q1 and +q2, and we hold q1 still, does q2 experience a repulsive force due to q1 repelling q2 AND a repulsive force due to q2 repelling q1? That is ##|F| = 2*\frac{k*q1*q2}{r^2}##
26. ### Find the Potential energy of a system of charges

There are six pairs. three turn out to be negative and three turn out to be positive (3q^2 - 3q^2) which nets zero when you add them together with the equation. But zero was the incorrect answer. Did I do something wrong? Thank you
27. ### Some confusion about work done to separate charges

The reason I'm posting this is because I'm confused about the reasoning behind the equation. For oppositely charged particles, wouldn't work done increase with distance? According to this equation you get a higher magnitude of work done the smaller the distance. How can that be? I got the answer...
28. ### I Force between Positive and Negative Electrical Charges

I have in the past been criricised for inappropriate postings that I could have resolved with research so this time I have done the research first. The best solution I have found is from wiki "that causes it to experience a force when placed in an electromagnetic field." What causes the force...
29. ### Two conducting spheres a distance d away with charges +q and -q

you can treat the center of two conducting sphere's like two point charges. Therefore it should be equal to ##k_e q^2/d^2##, but the answer is greater than ##k_e q^2/d^2##. Can someone explain how? Thank you
30. ### Electric field due to three point charges

I've calculated the intensity for every point charge which are EA = 6.741 x 10¹³ NC¯¹ EB = 4.494 x 10¹¹ NC¯¹ EC = 6.741 x 10¹³ NC¯¹ and I am pretty sure about this far but I am struggling to calculate the X-axis intensity and Y-axis intensity to find the entire approximate intensity with the...
31. ### Bound charges of a block (top and bottom surface)

From what I think, to find the bound charges of a block on the top and bottom surface I have to find the electric field or the displacement (D). However, I'm not sure how to proceed with a cube. For example, with a sphere ##E = \frac{Q}{4\pi \epsilon_0 r^2}## since r is constant. For a cube, it...
32. ### I Positive Charges: Explaining Motion Despite Net Force = 0

in a cours of electrostatic when we have a positive charge and we bring another one (also postitive)we have to do work and apply a force that equals the force of repultion over the distance which seems weird because if we do that the net force will be equal to 0 and the charge will not move can...
33. ### I Help with FLP argument of non-uniformly distributed surface charges

Hello, I'm reading FLP vol II, and I would appreciate some help to understand the argument supporting Figure 6-6. Basically they claim if a sphere has non-uniform charge distribution whose surface density is proportional to the cosine of polar angle, then this surface charge distribution is...
34. ### Understanding the electric force felt by the charges on a sphere

A thin shell in reality doesn't have zero thickness. Consider the image below, showing a cross-section of a small portion of the shell: Here we are considering a more general case in which we have electric fields of magnitude ##E_1## and ##E_2## on each side of the shell. Gauss's Law...
35. ### I An electrolytic capacitor charges by itself?

We've observed that an off the shelf electrolyte capacitor (330 μF) charges when it isn't connected to a current supply. Depending on the surroundings we get something between 10 and 100 mV potential across the capacitor. Does anybody know what's happening?
36. ### Electrostatic potential and electric field of three charges

So I started with b) and it there was no q2 this would seem reasonable I was wanted to ask , what effect does q2 have on potential of these two charges? Because it has to be given for a reason.
37. ### Electrodynamics: bound charges

I was trying to solve it using the formula for polaresation P = ε E - ε0 E. Then I tried to solve for E which is D/ε and D= ρf/ε. So at the end, I will have something as P = pf- (ε0ε). ρb = -∇ * P = 0 so σb = P * n = ...? I am unsure what the direction for the polaresation should be? I need...
38. ### I Charge in RLC circuit when starting charges are 2Q and Q

Hi all, I understand the standard solution where charge in an RLC circuit decreases from +Q to 0, for a capacitor with starting charges +Q and -Q. May I know what the terminal charge on a capacitor in an RLC circuit is, when it’s original charges are 2Q and 0? I am thinking it will be +Q and...
39. ### I Investigating the 1d Equation: Charges & Field Disparity

Can we apply the 1d equation (dE/dx = labmda/epsilon0)dEdx=λϵ0 to the first and the second figures? But, in the 2nd case, if we integrate the charge density, some field exists between the two charge densities. Intuitively, it should be like the last figure. What's wrong with this?
40. ### 2 Spheres of Charges and their Interaction

I can understand what happens with the conductor... (induction effects). But how can induction happen in insulators ? Is it due to the the induced dipole moment?
41. ### I How do point charges in a conductor move and stop?

Let's speak in the classical context (non quantum). We assume that point charges move in a conductor following Newtonian mechanics. How do point charges move along the boundary of the conductor and how do they stop (equilibrium) in the end?
42. ### I Moving charges in electrostatics

According to a popular book on electrodynamics a special case of electrostatics is- ''source charges are stationary (though the test charge may be moving)''. My question is- now that the test charge is moving, how is it a special case of electrostatics anymore? Also many times we deal with...

44. ### I Distribution of charges as a result of the Hall Effect

Circuit runs from q0 to q1, some E field (our charge source/sink) 1. Is the current running from q0 to q1 impacted by the existence of the B field? For example, if there were no B field, current would flow from q0 to q1, let's call it I0. When we flip on the B field what effect is there on the...
45. ### B Force between 2 Point Charges Across Frames

So, i was trying to calculate, the net force between 2 point charges in their rest frame, and in a frame where they are moving. So, assume, there are 2 point charges each of charge +q. They are r distance apart from each other and moving parallel to each other with a speed v relative to a lab...
46. ### 2 * 10 ^ 20 charges move in a wire when we connect a 3.7 V battery. Ho

W=Q*V 2*10^20 Q * 3,7 V= 7,4*10^20 ??
47. ### A copper wire contains 3.0 *10 ^ 22 number of charges on 1 meter wire

A copper wire contains 3.0 *10 ^ 22 number of charges on 1 meter wire. What speed do the electrons move when there is 2 A current in the wire. t=q/t=3,20*10^3 C/ 2.0 A = 1,5*10^22 s v= 1m/1,5*10^3s= 6,6*10^-4 m/s
48. ### Point charges in a regular hexagon

The answer should be (2×sqrt3×k×q^2)/a^2. What did I do wrong?
49. ### Do charges always lie on the inner surface of capacitors?

Parallel plates A, B are 5mm apart, with charges +1C and -1C respectively. Parallel plates C, D are 2mm apart, with charges +1C and -1C respectively. Capacitor CD is slid between capacitor AB. Find the potential difference between AB. The key idea to solving this problem is to suppose that +1C...
50. ### Principle of superposition for charges/induced charges

The key observation to solve the above problem is that the charge Q can be dragged out into a flat capacitor plate parallel to the 2 existing plates. Apparently, while the charge distribution on the 2 existing plates changes, the total charge induced on each plate remains the same, due to the...