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Questions tagged [charge]

A fundamental property of matter which causes it to experience electromagnetic forces.

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Why are there 6 interactions with 4 positive charges?

From a homework assignment, there are 4 spheres spaced 1cm apart. Each of the spheres are charged to +10nC and weigh 1 gram. The question wants us to find the final speed of the charges once they've ...
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If the cross-sectional area of a wire doubles shouldn't the current also double?

In this question the answer is B but I don't understand how that could be possible considering the area has doubled.
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When to use $e^{-t/RC}$ - Capacitor discharge and charge

Respected Team Members, I am learning how to calculate the amount of time it takes to charge/discharge a capacitor. The Formula given in the text book is $$\ V_{f}=V_{s}(1-e^{-t/RC})$$ But we ...
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Gauss' Law not including all of the system

Suppose we have a system of two parallel conducting plates charges $Q$ and $-Q$ and charge densities $\sigma$ and $-\sigma$. In this case, to find the electric field, Gauss' Law is used with a ...
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Proof of continuity of voltage across a capacitor

It is known that the voltage drop across a capacitor is a continuous function of time. This means that, for each instant t0, we may write: V(t0-) = V(t0+) This relationship is very used in the time ...
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What is the function $q$ in the definition of charge density?

Supposed we define $\lambda = \frac{dq}{dl}$. If I think of this intuitively, this makes sense; the linear charge density at a point is tiny amount of charge at that point divided by the tiny length ...
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Electrostatics, measurement of charge

How did physicists come up with a standard for measuring charge? How an electrical measurement of charge was made?
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Energy of the system of similar charges

We know that two same charges repel each other. To stop the charges from going away we have to exert an external force and hence energy is used. But if in a vacuum two similar charges are placed near ...
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The potential at a point

According to my book, 'The potential at a point is said to be 1 volt when 1 joule of work is done in bringing 1 coulomb charge from infinity to that point.' But I wonder how it is possible. As the ...
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The energy stored in capacitors in series [on hold]

If there is a capacitor of $2$ micro farad and $0.5$ micro farad in series and the charge on the combination of the two capacitors is $0.8\times 10^{-6}$ C. How would you find the energy stored on ...
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Conservation of Charge vs. Conservation of Energy

Is conservation of charge ever violated like conservation of energy is violated during cosmological expansion? I am trying to understand this with respect to Noether's Theorem.
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If voltage represents an energy difference between two points, why don't electronic appliances all use the same amount of energy?

As I understand it, voltage is an energy difference between two points. $$V_f - V_i = - \int \mathbf{E} \cdot d\mathbf{s}$$ But consider a toaster and a refrigerator each using their own 120V ...
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Gauss law in electrostatics

Consider a solid conductor,if the conductor makes a free electron inside that due to thermal energy ,so that causes one positive ion inside the conductor, my question is according to gauss law inside ...
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$E$ outside a Metal Spherric Shell with a off-center Point Charge inside Shell

If a charge +Q is placed inside a metal shell (NOT at the center), as shown below. I can understand that E will be 0 between inner surface and outer surface due to this is a conductor. Then according ...
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What's the electric field in a sphere with charge $Q$ and an inverse linear/square law density of charge?

In Classical Electrodynamics by Jackson problem 1.4 asks to find the electric field as a function of the radius of a sphere charged with a charge Q and with a spherically symmetric density that goes ...
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Is the centre of charge always within the centre of mass of an object?

What I am confused about is whether the charge of an object is concentrated within the centre of the mass itself, or does it change depending on the situation?
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How do we arrive on the same expression for Gauss's law when deriving it for a sphere or any other figure (say a cylinder)?

For a circular surface, the surface area of the circle is cancelled by factors in the denominator of $E$, leaving behind only $Q/\epsilon_0$. But what about when we conside a cylinder? How so we ...
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$CP$-transformation for spinor field. $C$ and $P$ do not commute?

I am bothered by an exercise about CP transformations where I get the result that CP acting on a Dirac spinor field is not the same as the PC transformation. The exercise states the following ...
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How to perform integration for all of space?

Two conducting spheres of radii $a$ and $b$ have charges $Q_1$ and $Q_2$. Distance between their centres is $R$. If ${\vec E_1}$ and ${\vec E_2}$ are electric field vectors due to the two spheres at ...
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Can one assume during the discharge of lightning, some energy is dissipated as heat? (High School Physics)

I was doing homework, and the following appeared as a question: A negatively charged thundercloud above Earth's surface may be modeled by a parallel plate capacitor. The lower plate of the ...
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Boundary conditions for an infinite line charge and grounded conducing plane

I'm not asking for a solution to the problem, I'm confused about what I should set the boundary conditions to, it's obvious that $V=0$ at $z=0$ because of the grounded $xy$ plane, but I don't know ...
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Best representation of a proton in non-static spacetimes

The classic way to represent a proton in flat spacetime is to use a simple point charge, $$J = (e \delta(r), 0)$$ But if we're using an arbitrary metric (let's assume still globally hyperbolic ...
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Poisson's equation and electric field interpretation

My question is this: Are all solutions to Poisson's equation for a certain charge density such that the negative gradient of them will give me the electric field? In deriving the equation, we say ...
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On the microscopic description of a steady electric current

In Purcell's Electricity and magnetism, page 137, the author derived a formula describing the average velocity $\overline{\textbf{u}}$ of positive ions inside a conductor, a gas made of neutral ...
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Does Gauss' law simplify even if charge density is dependent on angle?

We know that with Gauss' law applied to a charged sphere simplifies due to the symmetry of the sphere and we can take $E$ outside of the integral, but what if the charge density $\rho$ depends on ...
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Electric Field Lines between two equal charges end at the midpoint, violate rule that lines only start/end at charge/infinity

At the midpoint of the line joining two equal point charges, the field is zero, and the electric field lines on this line joining the charges each begin at a charge and kind of end at the midpoint. ...
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How can charge reside inside a solid sphere of charge?

I was studying the electric field and potential of a solid sphere of charge. In my textbook it is mentioned that we distribute electric charge in the interior of the sphere. I had learnt that in a ...