What is Charge: Definition and 1000 Discussions

Homework Statement Prove that the Noether charge ##Q=\frac{i}{2}\int\ d^{3}x\ (\phi^{*}\pi^{*}-\phi\pi)## for a complex scalar field (governed by the Klein-Gordon action) is a constant in time. Homework Equations ##\pi=\dot{\phi}^{*}## The Attempt at a Solution...

At this point I was given rho, sigma and landa to hold value of these three different kinds of density ρ = Charge/Volume -------------- Volume Density σ = Charge/Area ----------------- Area Density λ = Charge/Length ---------------- Length Density How do I know which type of density to use over...

and two -q charges aligned along the x-axis as follows... -q__________q__________-q <--- the space between them being d a) Suppose the +q charge is displaced perpendicularly by a small vertical distance dy. What is the total force F acting on it? Taylor expand your answer to leading order in...

Homework Statement Consider the charge distribution of a uniformly charged ring of radius ##R## and charge ##Q## at a distance ##d## above the origin and a uniformly charged ring of radius ##R## and charge ##-Q## at a distance ##d## below the origin. (a) Calculate the dipole moment of this...

Note from mentor: this thread was originally posted in a non-homework forum, therefore it lacks the homework template. I was wondering if the electric charge density ##\rho({\bf{r}})## of a point charge ##q## at position ##{\bf{r}}_{0}## is given by...

Homework Statement A small object with mass m, charge q, and initial speed v0 = 6.00×10^3 m/s is projected into a uniform electric field between two parallel metal plates of length 26.0 cm(Figure 1) . The electric field between the plates is directed downward and has magnitude E = 600 N/C ...

Hello! I am bit confused about kirchhoffs law with capacitors. So if I have a battery and resistance, I obtain V-RI=0. But from what I read, if I have a capacitor and resistance (so discharging capacitor), the equation reads R(dq/dt) + q/c = 0, which is equivalent to RI + q/c =0. Why in this...

Homework Statement Homework Equations Work = - (integral of) (E dot dl) The Attempt at a Solution Hi, I know that the right answer is D zero, but I fail to understand why. I said that the answer was A as I have different charges, and I thought that depending on how I approach each...

Homework Statement Two particles 1 and 2, each carrying 6.0 nC of charge, are located along an x axis, one particle atx=−30 mm and the other at x = 30 mm. Where along the y-axis is a particle 3 carrying a charge of +2.0 nC if it experiences an electric force of 6.9 × 10^−5 N ȷ^? Homework...

Homework Statement I did a lab involving Van de Graaff generator. Basically, below the charged sphere, I put a neutral sphere on a scale and measure the difference in mass which then I can calculate the force acting on the neutral sphere. I repeated the experiment with different distance. What...

1) If I vary charge densities, but keep current density constant, do I get any sort of electromagnetic wave? 2) If the answer to question 1 is no, then if I vary charge densities, but keep current density constant, could I conceivably have a two isolated "open circuit" current elements of...

Hello Ads say a gyroboard with the battery 48V 4.4AH, and the motor 700 Wt will run for 2 hours at the speed of 20km/h ! But - simple physics - will not the motor drawing about 10-15 Amp exhaust the battery in just some 20 minutes !? Do ads lie ?

Sorry I couldn't finish the title. I ran out of space. Anyway, here's the question: A uniformly charged, infinitely long line of negative charge has a linear charge density of -λ and is located on the z axis. A small positively charged particle that has a mass m and a charge q is in circular...

Homework Statement Four uncharged metal plates of the same area are placed in vacuum and separated by equal distances. They are connected by conducting wires to two resistors, two open switches and a battery. The thickness of the plates is negligible, and their area is sufficiently large. S1 is...

Homework Statement When a -2C is moved from point A to B, the potential energy of the system increases by 10J. What is the voltage V(ab)? Homework Equations U=qV The Attempt at a Solution 10=(-2)V, I thought the voltage was -5V but the correct answer is +5V. Could someone explain why this is?

Homework Statement In a cubical volume, 1.05 m on a side, the electric field is given by the formula below, where E0 = 1.25 N/C and a = 1.05 m. = E0(1 + z/a) i + E0(z/a) j The cube has its sides parallel to the coordinate axes, see the figure. Determine the net charge within the cube...

Homework Statement Suppose the nonconducting sphere of Example 22-4 has a spherical cavity of radius r1 centered at the sphere's center (see the figure). Assuming the charge Q is distributed uniformly in the "shell" (between r = r1 and r = r0), determine the electric field as a function of r...

So why do Quarks have fractional non-discrete charge? Wouldn't it just be easier to just define ##\frac{1}{3}e## as +e and vice versa to preserve the discreetness of what we define as e?

is there any way to fully neutralize a charged metal plate ? connecting it to metal body of relatively huge capacitance will make its charge negligible but not zero? is there any other way?

The other day we were working on a problem which stated : Q charge is given to the positive plate of an isolated parallel plate capacitor of 10 μF. Calculate the potential difference betweeen the plates. Our teacher said that as the plate is isolated, Q charge will be divided between the two...

Homework Statement Two identical balls (B and C) with a mass of .5 g are suspended from two strings as shown above. The balls carry equal charges +10nC each and are separated by a distance of 4 cm. A. Draw the free-body diagram and show all forces applied to ball C. B. Find the tension force in...

Homework Statement A positive charge Q1 = 7.4 μC is located at a point X1 = -2 m, a negative charge Q2 = -9.7 μC is located at a point X2 = 3 m and a positive charge Q3 = 2.1 μC is located at a point X3 = 9 m. Draw free body diagrams for the electric force acting on Q1, Q2 and Q3. Find the...

Homework Statement A semi-circle of radius R has a charge Q uniformly distributed over its length, which provides a line charge density λ. Determine E at the origin. Homework EquationsThe Attempt at a Solution https://www.physicsforums.com/attachments/105239 I can tell by argument of...

Homework Statement Homework Equations There are no equations here, only theoretical knowledge The Attempt at a Solution Hi, My approach was this: I know that with the positive charge on the sphere being lowered into the cup I will have the inner area of the cup have a negative charge and...

Having read several introductory notes on Gauss's law, I have found it very frustrating that when the author comes to discussing the standard examples, in which one considers symmetric charge distributions, they do not explicitly discuss the symmetries of the situation, simply stating that, "by...

So the potential inside a conductor is constant. Does this mean that if there were a conductor, B, inside another conductor, A, the charges of A/B would redistribute such that the electric field inside would be zero (hence constant potential)? This seems logical but a bit too easy? Also, if it...

I've been looking through the internet and so fair I haven't found anything too clear on this. Some articles have said that plasma can be affected by magnetism and can be conductive, but my question is, will it become positively/negatively charged while current is flowing through it, and if it...

Homework Statement There's a uniform infinite line charge with the charge density λ. A point particle with charge q moves with a velocity v parellel to infinite line. What is force exerted on point particle? What is magnetic field seen in ths moving frame(particle frame)? Homework Equations...

You have two electrons held at a fixed distance X from each other. You measure the opposing force is Y. Now you bring the electrons closer to each other, and then let them go so they can fly apart. As the electrons move apart and reach distance X, will the opposing force still be Y, or will it...

The electric field inside an uncharged metal sphere is initially zero. If the sphere is the positively charged, the field at the center of the sphere will be...?

Hello, I have recently bought 4 cylindrical lithium ion batteries from hobby king to make a battery pack. To do this, I put all 4 of them in Parallel, so that the voltage would stay the same, but the capacity would increase. It says on Hobby king that they can charge at 5C, and since they are...

Homework Statement [/B] Two conducting spheres are far apart. The smaller sphere carries a total charge Q. The larger sphere has a radius that is twice that of the smaller and is neutral. After the two spheres are connected by a conducting wire, the charges on the smaller and larger spheres...

A charge moving relative to some observer produces magnetic field in space around it. Now I want to ask that how does the magnetic field of the charge at any fixed point varies as the charge passes by. Or is the B field only dependent on current and not a single moving charge? If I introduce...

So far I have came to know that when a charge is accelerated the electric field magnitude around the charge changes and the effect is not felt instantaneously. The change in magnitudes of electric and magnetic field travels outwards at speed of light creating the so called EM wave. So the EM...

Homework Statement It is known that the potencial is given as V = 80 ρ0.6 volts. Assuming free space conditions, find a) E, b) the volume charge density at ρ=0.5 m and c) the total charge lying withing the closed surface ρ=0.6, 0<z<1 Homework Equations E[/B]=-∇VThe Attempt at a Solution (this...

My question is, Why do we use q=1.6*10^-19 C rather than -1.6*10^-19 C, for the charge on an electron in most of the equations?

Can Kaluza-Klein theory accommodate magnetic charge? If so is there a simple geometric difference between electric and magnetic charge in such a theory? Thanks!

Hi. A student wishes to test gravitational time dilation near a black hole within her lifetime, so she travels to a location where a black hole is said to reside and parks her ship at distance where she is not affected by the hole's time dilation effects. She then fires a tethered capsule...

Hello, Given a simple electric circuit like the one below (taken from Wikipedia) If we were to start from tracking all the forces acting on each individual free electron in the circuit, would it be possible to eventually find all the currents and voltages acting in the circuit? Probably a...

Homework Statement A point charge of 5.6 microcoulombs is placed at the origin (x=0) of a coordinate system, and another charge of -1.9 microcouloumbs is placed on the x-axis at .29m. Where on the axis can a third charge be placed so that it experiences no charge? q1= 5.6 E-6 q2= -1.9 E-6 d=...

Light is an electromagnetic wave and to be so it needs an oscillating electric field, so only charges that undergoes harmonic motion shold be able to generate light is that right? And if that's right how can an electron that goes form an excited state to a lower one emit a photon? It wasn't...

Homework Statement This is more of a general question, but a simple example would be find the force on a test charge q at the center of a ring of charge with a total charge Q and a charge distribution given as λ(θ) =ksin(θ) where θ is measured clockwise with respect to the positive x-axis. The...

In the situation consisting of a steady current of 1A in an arbitrary closed path, what would the consequences be for the electric field if the drift velocity was non-uniform along the path due to non-uniform carrier density? This would be a case of a "uniform" 1 amp, but where the charge...

In any simple carboxylic acid there are two oxygen atoms then i have a confusion that which oxygen has more negative charge on it or which one has the most electron density on it?

I understand what we classically know as the charge of a particle is actually the parameter of the local phase symmetry of the field the particle belongs to, the Noether current of which permits its coupling to the electromagnetic field. But when a field has phase symmetry it is symmetric under...

I am having a hard time understanding flat band voltage in MOS capacitor. Please see the picture below about MOS capacitor. Q0 is a fixed effective charge at the surface between oxide and semiconductor and it is positive here. The voltage across the oxide caused by the fixed charge ψox =...

Homework Statement An insulator is in the shape of a spherical shell. The insulator is defined by an inner radius a = 4 cm and an outer radius b = 6 cm and carries a total charge of Q = + 9 C (1 C = 10-6 C). You may assume that the charge is distributed uniformly throughout the volume of the...

Formula for Electrostatic Potential due to a point charge is V=1/4π∈ Q1 Q2/r This implies that at r=0 value of the potential should be infinity. Is it True. If that is the case then how we say the terminals of a battery having positive and negative charge are having definite value of...

Homework Statement Is it possible to introduce local charge on a conductor? Homework Equations - The Attempt at a Solution I know that electrons can move freely from atom to atom in the conductor, so if you introduce excess electrons to the conductor, they'll spread out and there won't be a...

Greetings, There seems to be a supposition in astronomy that charged black holes are uncommon. Is this assertion well supported? According to a paper I found by Briet and Hobill, if you look at gravitational lensing alone charged black holes look just like regular black holes, but with a mass...