Dielectric Definition and 731 Threads

Homework Statement Show the the induced charge density on a dielectric placed inside a capacitor is given by $$\frac{k-1}{k}\sigma$$ where ##\sigma## is the charge density of the capacitor plates and ##k## is the dielectric constant. Homework Equations $$E=\frac{E_0}{k}$$ The Attempt at a...

Can a rotating dielectric disc be polarized? No external electric or magnetic field .

I saw an experiment the other day, where a van de graaf generator charges up this big smooth chrome sphere. There is a "wand" with a much smaller sphere nearby that's grounded, and periodically a spark can be heard and seen when the big sphere dischrages to the wand, which corresponds to...

Why do capacitors need dielectrics (insulators) in between the two plates(conductors)?What if there is no dielectric in capacitors ?Function of a capacitor is " a capacitor stores energy in the form of an electrostatic field between its plates" Let's say there is a conductor is between them...

Homework Statement Homework EquationsThe Attempt at a Solution for #14, I remember a battery maintains the potential therefore, V should be constant; dielectric increases charge on plates and increases capacitance but I couldn't find an option that matched. The answer key says "d" but I...

Homework Statement Determine the conductivity of the insulator in a spherical capacitor filled with weakly conductive dielectric. Specific conductivity of the dielectric is λ, the dielectric permittivity ε. Ansver in book is ##\Lambda = \frac{4\pi\lambda}{\epsilon} \frac{R_1R_2}{R_1-R_2}##...

Homework Statement 2 concentric conducting spherical shells, with radii a and 2a, have charge +Q and -Q respectively. The space between the shells is filled with a linear dielectric with permittivity ε(r) = (ε0*a)/(1.5*a - 0.5*r), which varies with distance r. a) Use Gauss's law to determine...

Problem: When a dielectric slab is inserted between the plates of one of the two identical capacitors in Fig. 25-23, do the following properties of that capacitor increase, decrease, or remain the same: (a) capacitance, (b) charge, (c) potential difference (d) How about the same properties of...

Consider the problem shown in the "wave_incidence_1.png" attached image. An electro-magnetic wave is traveling towards an interface between its current medium and a new medium, which has a refractive index n_2 \neq n_1. The interface is represented by the (x,y) plane. The electric field...

Two capacitors (lets call them C1 and C2) in series are connected to a voltage source and charged. While still connected to the source one of them is filled with a dielectric (lets say C2 is filled). I know the charge on C2 will change by a factor of K because the source keeps the potential...

Homework Statement http://postimg.org/image/vzhqi8er5/ Homework EquationsThe Attempt at a Solution I understand all the calculations here - http://www.physicspages.com/2012/10/18/coaxial-cable-with-dielectric/ I have one issue that is bugging me though - if λ charge density is distributed over...

Homework Statement A realistic capacitor is almost always filled with dielectric, but invariably this dielectric will conduct just a little, and the charge stored on the capacitor's plates will "leak." Over time, quite a bit of current can leak away. A good capacitor has a small leakage...

Homework Statement I have a lab where I have to use two methods to find the capacitance of printer paper. Homework Equations C = kAeo / d The Attempt at a Solution From these slopes, I got k = .897 for the first type (using changing distance between the plates of the capacitor) for the...

Hi everyone, I just wanted to know/understand that, why do the dielectrics don't get polarized, when subjected to induced electric field ? Because, according to the definition of electric field(which is a vector), it is the force per unit charge, which implies, that electric field has a unique...

Homework Statement When a dielectric is partially inserted between two plates of a capacitor that is disconnected, what will be it's motion? Also what will be its motion if the capacitor is connected to a battery? Homework EquationsThe Attempt at a Solution For the first part. I think the...

Homework Statement A capacitor connected to a battery initially holds a charge of +q on its positive plate and -q on its negative plate. The electric field between the plates is initially E. A dielectric material is then inserted that polarizes in such a way as to produce an electric field of...

What is Dielectric confinement effect?. or could you advise me literature about this? Thank you.

Ok so my question(s) has more than one part. First, the energy stored in capacitor is ##(1/2)CV^{2}## , is the ##V## the voltage of the source that charged the capacitor?? If I had two identical capacitors, and charged one using a 9V source and one using a 12V source, would the one charged by a...

Homework Statement (a) Calculate the Electric displacement of parallel plate capacitor of with a thickness d (in z), and length L (in x), and a width W (in y). Within the capacitor is a dielectric oil with a dielectric constant –εr , and the charge on the plates is ± q. (b) Using the...

Why is the dielectric constant smaller in few-layer materials than in bulk materials?

I want to build high voltage feedthroughs (vacuum) from epoxying pieces of alumina together, and then epoxying alumina strips on the outside to cover the spaces between. Can I use JB weld, as far as things go electrically? People have reported that JB weld is unexpectedly wonderful for vacuum...

Let we have a dielectric with field ##E## inside and with a little hole. I have problem. I get a two different answers on this problem, and I try to understand which one of them correct. As mentioned in http://www.feynmanlectures.caltech.edu/II_11.html#Ch11-S4 (11.25), the electric field in...

As far as I am concerned, dielectric function can be computed by band structure. However, band structure is a global property of solids, while dielectric function is a local property. How a local property can be computed from a global property. Put it another way, if I want to calculate...

Homework Statement Please see attached. Homework EquationsThe Attempt at a Solution I get a result of ## \alpha =\frac{1}{2} ## for part a) - which I think is correct. I'm stuck however on part b) - with the dielectrics. I have that the field in the region where the dielectric is ##E_{1}##...

Hi everyone. I have a problem with my device. It consists of a parallel plate capacitor with plates made of galvanized iron. Each plate's area is 1mx1inch. It's connected to a bleeder resistor and basically, the circuit is just a simple RC circuit. The source I'm using is a constant 5V DC...

Homework Statement A capacitor is charged to V = 5 kV. A wire is then connected to one plate and is slowly connected to the other. Before actually touching the plate, a spark of length l = 1 cm shoots from the wire to the plate. Using this information, estimate the dielectric breakdown of air...

Hey, we have learned in class that if you partialy insert a dielectric slab into a capacitor where voltage is held constant, there is a force pulling the dielectric farther into the capacitor. This gets me consfued. I know the more dielectric material there is in the capacitor, the capacitence...

Homework Statement What is the magnitude of the electric field due to a 6.0 x 10-9 C charge at a point located 0.025m from the charge? The charge and the point in question are located underwater (κ(water) = 80). Homework Equations I know that E = magnitude of electric field = kq/r2, where k =...

Which of them 1.Polar Dielectric molecule 2. Non Polar molecule Will get polarized to a greater extent when kept in a uniform electric field? (I think its the 2nd one because force applied has to stretch the positive and negative charge centres apart to polarise it.. But at the same time for...

Hi. According to classical electromagnetism (and common sense) the intensity of a beam of light entering a dielectric medium should remain constant. Hence the length of the poynting vector must remain constant. But how do you derive mathematically the last point? Because if you just replace...

Homework Statement Griffiths was trying to prove that when calculating the electric field inside a dielectric, we may assume the dipoles induced in it are "pure" dipoles, although they are in fact "physical" dipoles, as long as we view the field as a macroscopic field, one that is averaged over...

Say you had two needles sticking out of an insulator in an air-filled chamber covered by an aluminum foil cup. The needles are charged to a high enough electric field to cause dielectric breakdown of air. Will a spark go from needle to needle? Or will the needles cause an induced negative charge...

Original Problem: "A sphere of radius a is made of a nonconducting material that has a uniform volume charge density [PLAIN]http://jkwiens.com/2007/10/24/answer-electric-field-of-a-nonconducting-sphere-with-a-spherical-cavity/d2606be4e0cd2c9a6179c8f2e3547a85_2.gif. A spherical cavity of...

Ponderomtive force is well known phenomenon, able to accelerate particles of all charges in plasma, but what about neutral gas? If we omit thermodynamics for a while and consider a perfectly non-ionizable gaseous dielectric, would polarisation be enough to induce motion in it? Thanks for...

Homework Statement I've not been able to do this question for years so I'd really appreciate some help. Light is normaly incident from a medium 1 with impedance Z1 through a layer of medium 2 of thickness L and impedance Z2 into medium 3 of impedance Z3. Obtain an expression for the total...

In my textbook it is written that Electric charge on plates of capacitors (without dielectric ) is Q=CV And when dielectric is inserted in the space between plates of capacitors .charge Q remains the same whereas values of C and V change. i.e Q=C'V' is it correct?

suppose a battery connected to a capacitor only (and no dielectric inserted), the potential difference of the capacitor will increase till it becomes equal to that of the battery, suppose we put dielectric in the capacitor, this will decrease potential difference of the capacitor, now the...

Homework Statement An infinitely long dielectric cylinder with radius R and relative permittivity ##\epsilon_r## contains a free charge density given by: ##\rho(s)= ks## for s<R and 0 for s>R, where k is a constant. Find the polarization P and any volume or surface polarization charge...

Homework Statement Consider a parallel-plate capacitor, with two square plates of side \mathrm{12.0 cm} separated by a \mathrm{4.50- mm} gap. Half of the space between the gaps is filled with a material of dielectric constant \mathrm{K = 3.40}, while the rest is filled with just air. (a) What...

Homework Statement 2. Homework Equations [/B] I am trying to prove the equation $$ \frac{\bar{P}}{V}=\frac{1}{2}E_0^2\sigma_{AC} $$ which can be rewritten as $$ \begin{align} \frac{\bar{P}}{V} &= \frac{1}{2}E_0^2\sigma_{AC}\\ &=\frac{1}{2}E_0^2\ \omega\ \epsilon_0\ \epsilon^{''}_r\\...

Homework Statement Homework Equations Coulomb's law : F=q1q2/4πεr2 where ε=εoK The Attempt at a Solution Suppose there is a dielectric slab of thickness 't' and dielectric constant 'K' inserted between the charges separated by a distance 'r' ,then if we convert the slab thickness to its...

Odd question, would anybody know what would happen if a parallel plate capacitor (good conductor) had a soft magnetic material (fairly poor conductor) as a dielectric? What would be the DC/AC electrical characteristics of this?

Homework Statement A cylindrical distribution of charge ρ = α/sqrt(r) where α = 2 µC/m^(5/2) extends from 0 cm to 9.3 cm (has radius 9.3 cm). Concentric with this is a dielectric shell with k = 5.44 of inner radius 16.6 cm and outer radius 24.9 cm. What is the electric field at 3.53 cm, 12.6...

Homework Statement A parallel plate capacitor with plate area A = 100 cm^2 and plate separation of d = 5mm is connected to a 120 Volt power supply and allowed to fully charge. a) Calculate the capacitance, stored charge, electric field midway between the plates and potential energy stored...

Hi all, I am wondering how is it possible that the polarization effects of a dielectric material remain confined inside the material itself. That is: for a LIH dielectric, the equations state that the electric field inside the material is reduced by \epsilon_r. But outside the material, no...

Homework Statement Two identical capacitors Ca and Cb each of capacitance 6.60 http://lon-capa.mines.edu/adm/jsMath/fonts/cmmi10/alpha/100/char16.png F are connected in parallel across a CONSTANT total electric potential difference of 480 V. A dielectric slab of dielectric constant 4.65 can...

Hi I have a the problems! i need this materials for dielectric : 1.pvc (Kg) 2.dop (Kg) 3.carbonate (kG) so, i Specify this propertise for dielectric : 1.T(Tensile strength) =16 2.E(elongation) =300 3.Density=1.45 4. H(Hardness)=78 now, I need to...

Is there a creditable chart out there - on the dielectric constant of gases? What is the dielectric constant of Sulfur hexafluoride (SF6) compared to other gases or other gases in a vacuum? Thank You

1. The problem statement, Dielectric plate is placed in capacitor to the half(picture) and it can freely move. Capacitor consists of two parallel plates and is isolated. Consider two cases: a)charges on plates are constant, b)voltage is constant. What happens in each case? 2. Homework...

Suppose AC current is shooting into a wire, and the wire is attached to a bulk piece of metal off to the side of it, kind of like a ground, but not as deep as a ground. Wouldn't the bulk piece of metal work kind of like a capacitor and smooth out the voltage a bit? Everywhere I Google, I see the...