# What is Elecrostatics: Definition and 101 Discussions

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1. ### The equipotential surface of a system of two unequal charges

We have a system of two unequal oppositely charged point charges, of which ##q_2## is smaller and ##d## is the distance between charges. There is an equipotential spherical surface of potential ##V=0## that encloses a charge of lesser absolute value. The task is to find parameters of that...
2. ### B When a charge moves with respect to a second charge, does the electric field change?

So consider you have a point charge ##q_1## which is somehow fixed in space so it won't move if a force is applied to it. Then at some distance away you have another point charge ##q_2##, where ##q_1## and ##q_2## are of comparable magnitude (so, one is not insignificant compared to the other)...
3. ### Potential at a point inside a solid non conducting uniformly charged sphere

My friend said 'you missed the negative sign the second time you wrote integral of Edr in the right hand side in your second line'. But if put a negative sign it would mean that potential decreases when travelling against ( antiparallel) to field, which is wrong
4. ### B Why don't electrons leave a metal surface?

Why don't electrons leave the metal surface? I have searched the internet for the answer and from my teachers they all say that electrons are attracted to the positive ion crystal lattice. I know that, but the problem is why is that attraction so much greater than the repulsion from other free...
5. ### B Frequency of EM Waves from Monitor for Black/White & Color Images

I am using an old monitor (MITSUBISHI RDT27IWLM). The power consumption changes when the screen is white or black, but does the frequency of the weak electromagnetic waves emitted from the monitor change? Or is the frequency the same, only the output is stronger/weaker?

29. ### The vector sum of the electric forces exerted on a particle

r_{13}=r_{23}=\sqrt{(30*10^{-3})^2+(90*10^{-3})^2}=\sqrt{9*10^{-3}}\\ F^E_{13}=F^E_{23}=9E9\cdot\frac{5*10^{-9}\cdot3*10^{-9}}{9*10^{-3}}=1.5*10^{-5}\\ \theta=tan^{-1}(\frac{90*10^{-3}}{30*10^{-3}})=71.565\,degrees\\ \vec{F}^E_{13}=<F^E_{13}cos\theta, F^E_{13}sin\theta> = <4.743*10^{-6}...
30. ### Exploring the Interaction of Magnetic and Electric Fields

Hello, If you have an appropriately oriented conductive ring in a constantly changing magnetic field, current will flow in the ring. There will also be a magnetic field associated with the current in the ring. I understand (maybe ... ) that the current is due to the electric field which is...
31. ### Kirchoff's laws and capacitance

Equivalent capacitance before and after remains the same. Now the 10F capacitor (which was initially connected in parallel with 20F) would have 30 C charge. Hence an additional 20C must have been supplied to it. The only path which may supply the charge is through battery. However this leads...
32. ### Point Charge above an Infinite Plate

Merged thread deleted first post next post is the first post.
33. ### 3 concentric conducting spheres, the outer one connected to ground

What would the fact that the fifth surface is connected to the ground imply: that V(r=R_5)=0 or that \sigma _5=0?
34. ### Electrical potential of a thin wire in an E field

Assume that an infinite metallic plate A lies in the xy-plane, and another infinite metallic plate B is parallel to A and at height z = h. The potential of plate A is 0, and the potential of plate B is constant and equal to V. So, there is a uniform electrostatic field E between plates A and B...
35. ### Why does the potential of A decrease when plate B is nearby?

Summary:: if Plate A had a potential of 9V, This means as We approach a unit charge from +Infinity to A we have to do this precise amount of work Now we remove plate A, And replace it with plate B that has a potential of -9V Again that means to go from +Infinity To B we actually gain energy, or...
36. ### What would happen to a charge that is placed in an Electric Field = 0?

If a charge was placed inside an electric field, where the electric field was equal to zero, what effect would the charge have?
37. ### Electromagnetic plane waves from a current sheet

I have an infinite sheet (in lossless, homogeneous medium) of time-harmonic current in ##yz##-plane at ##x=−d##. The current density on this sheet is given by $$\mathbf{J}=\hat{z}J_0\delta(x+d)$$ ##δ(x+d)## is delta function. Moreover, there is a perfect electric conductor (PEC) half space at...

39. ### Electric field due to two positive charges

I am having trouble solving the following problem. I am given two positive charges on the x axis: I know that the electric field strength at point P is ##E=150 \frac{V}{m}##, ##d=1.8m## and ##a=2.5m##. I want to find the charge of ##Q##. As far as I know, the electric field on the y-axis...
40. ### 1D Green function for a charged layer

I came across an example of a solution to finding the potential of a charged layer using the Green function (here, pdf). The standard algorithm for finding the Green function by boundary conditions for many problems is understandable: \begin{align*} G_\mathrm{Left} = Ax+ B \\ G_\mathrm{Right} =...
41. ### Finding the induced EMF in a solenoid-wire system

I know that ##B = \mu n I## and ##\phi = B \pi R^2##. So with have ##d\phi / dt = \mu n \alpha \pi R^2##. But I don't know what to do with this? is this the answer? I don't think so but I don't know what to do after this.
42. ### I Determining continuity using Gauss' law

I know how Gauss law helps us to calculate the discontinuity at a point on the surface of a surface charge. Similarly using Gauss law, is there a way to determine the continuity at other points of electric field due to a surface charge or the continuity at all points of electric field due to a...
43. ### Why is the x-component of the electric field at point P positive?

I got the answer: E(P)=(k*Q)/(3î )−(k*Q*ĵ) /2 Can someone confirm if this is the right answer?
44. ### What is the continuous electric dipole distribution?

An electric dipole is a system of two opposite point charges when their separation goes to zero and their charge goes to infinity in a way that the product of the charge and the separation remains finite. Now how can we have a continuous electric dipole volume distribution from such a...
45. ### Electric potential difference between a battery's + terminal and the ground

Hi, I've a question about electricity in the following scenario: consider an accumulator (e.g. a 9V battery) and an analog/digital voltmeter having a probe connected to the accumulator + clamp and the other to the ground (for instance connecting it to a metal rod stuck in the ground). Do you...
46. ### Induced charge on a conductor

Homework Statement Imagine having a conducting sphere with free charge ##Q## surrounded by a spherical shell filled with a dielectric and then a conducting spherical shell with no free net charge. I want to find out the charge induced on the spherical conducting shell by the sphere or by the...
47. ### Spherical capacitor with dielectrics

Homework Statement Consider the following system: which consists of a conducting sphere with free charge , a dielectric shell with permittivity ##\epsilon_1##, another dielectric shell with permittivity ##\epsilon_2## and finally a conducting spherical shell with no free charge. Homework...
48. ### Corollary of the Uniqueness Theorem in Electrostatics

Following my instructor's notes the statement of the Uniqueness Theorem(s) are as follows "If ##\rho_{inside}## and ##\phi_{boundary}## (OR ##\frac{d \phi_{boundary}}{dn}## ) are known then ##\phi_{inside}## is uniquely determined" A few paragraphs later the notes state "For the field inside...
49. ### A challenging capacitor problem

1. Two identical flat plate capacitors are inserted in each other. First, none of the plates was charged, but then they have been connected to sources of current, keeping the constant voltage ## V_1 ## and ##V_2 ##. Find the potential difference between inner plates, which are kept at the...
50. ### Energy of a material with permanent polarization

In electrostatics, for what I understand the when I have an electric field, the density of the energy stored in it is given by the following formula: $$W = \frac{1 }{2} E \cdot D$$But when there is some material permantent polarization the above formula fails to work. Is this correct? How can...