# Tag Info

### Are Maxwell's laws mathematically precise?

The title of the question asks if Maxwell's equations are mathematically precise. The answer is certainly yes. Maxwell's equations are well-posed differential equations. There is no ambiguity about ...
• 51.5k
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### How can photons have an electric field without having a charge?

I believe electric fields can only be created by charged particles There are two things that can produce a (disturbance of the) electric field: A charged particle A changing magnetic field Since ...
• 28.5k

### Why doesn't the voltage increase when batteries are connected in parallel?

tl;dr Batteries do not create electric fields to move charges. They move charges, which creates electric fields. a battery [...] gives out some electric field that moves through the circuit and gives ...
• 561
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### Is force due to electric field instantaneous? If not then why?

No two things in the universe happen "instantaneously", unless they are at exactly the same location, because "instantaneously" would have different meanings for observers moving at different ...
• 24.8k

### How is energy "stored in an electric field"?

This question is deeper than you might expect. Neither energy nor an electric field is exactly what you might expect. First, physics is a description of the behavior of the universe. It is not the ...
• 41.7k

### How can electric fields be used to detect cracks in metals?

Cracks and other flaws can be found in metal parts by scanning the surface of the part with a small electromagnetic coil, which induces a current flow in the metal part as if the coil and the part ...
• 96.2k
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### Purpose of Using Taylor Series and Multipole Expansion to Approximate Potential

What does the electric potential of a water molecule look like? Imagine a cartoon picture of a water molecule, in which the oxygen atom has charge $-2q$ and sits at the origin and the hydrogen atoms ...
• 70.3k
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### If we remove all electrons from a conductor, how can the positive charge rearrange itself?

If you suddenly removed all the electrons from a piece of material, or even just the valence electrons, you would be left with a huge concentration of positive ions in a small volume, which would ...
• 134k
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### Can a magnetic field exist without an electric field present?

The "magnetic field" is a concept within classical electrodynamics. Maxwell's equations were developed in the mid 19th century at a time where basic atomic physics was still a nascent field of study. ...
• 4,181
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### What happens if you use a battery to charge up a capacitor fully, and then disconnect the battery, where does the charge 'go'?

The charge won't go anywhere and the capacitor will remain charged until you short the plates of the capacitor. Where there was once a battery terminal there is now an insulator and that stops the ...
• 1,297

### How can neutral atoms have exactly zero electric field when there is a difference in the positions of the charges?

If something is 'Electrically neutral' this means that the algebraic sum of its electric charges, however distributed, is zero. This does not imply that there is no electric field in its vicinity. ...
• 36.1k
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### Are the plates of a battery really charged?

I think that most confusion about batteries comes from ignoring the electrolyte. For example: Zinc has 2 valence electrons. So it wants to get rid of them. To do so it sends them to the copper ...
• 104k
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### How can neutral atoms have exactly zero electric field when there is a difference in the positions of the charges?

It is said that atoms with the same number of electrons as protons are electrically neutral, so they have no net charge or net electric field. This is a great over-simplification, which I am sure you ...
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### Do extremely high-voltage power lines emit positrons?

Your analysis doesn't make sense because the units don't match up. $1100 \, \text{kV}$ is not more than twice $510 \, \text{keV}/c^2$, because the two quantities can't be compared at all. It's like ...
• 103k

### In what sense, physically speaking, are electric and magnetic fields perpendicular?

The electric and magnetic fields are generally not perpendicular. Presumably you're thinking of electromagnetic waves propagating in vacuum, in which case the electric and magnetic fields are ...
• 70.3k
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### How does energy flow in a circuit? Which is correct?

This is a fantastic question, that indeed has a fantastic answer. I would like to answer your question by answering 3 other apparently disconnected questions, but then we'll connect them that will ...

### Why doesn't the voltage increase when batteries are connected in parallel?

Think of a battery as an escalator (potential gravitational energy and potential electric energy/voltage are analogous here). If you have two escalators side by side, taking either one will get you to ...
• 7,698
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### Why is electric flux through a cube the same as electric flux through a spherical shell?

Consider the flux through a tiny segment of a sphere. Since the electric field is parallel to the normal of the surface at all points, the flux is simply the electric field at that distance multiplied ...
• 2,111

### If electric field inside a conductor is always zero, then why do free electrons move?

The electric field is only $0$ in the electrostatic case. That is, the field is $0$ when no electrons are moving. Suppose it was not $0$. Electrons would feel a force and move in that direction. This ...
• 41.7k
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### Why do electric field lines curve at the edges of a uniform electric field?

I have taken your image and created a few additional field lines at one end of the plates in the first diagram below. When you come to the ends of the plates, the field starts to resemble that ...
• 74.5k
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### How can I prove that a state of equilibrium is unstable?

In the centre of a bowl there is equilibrium. Put a ping pong ball in it. If this ball is ever shaken slightly away from equilibrium, it will immediately roll back. A "shake-proof" equilibrium is ...
• 51.6k
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### How can electric field be defined as force per charge, if the charge makes its own, singular electric field?

It's true that a point particle with finite charge is problematic in electromagnetism because of the infinite field and associated energy near such a particle. However, we don't need that concept in ...
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### How does the speed of electricity become the same as the speed of light?

If there are charges being setup in the wire, the charges(electrons) have mass and cannot move at C. How then they don't affect the speed of electricity and gives us its speed to be equal to C. They ...
• 104k

### Potential Nonsense

You are correct in your reasoning. However, that line does have a voltage equal to $0$. The trick comes in from the fact that $V=0$ doesn't mean $\vec{F}=\vec{0}$. The force depends on the change in ...
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### Apparent violation of Gauss Law

As far as I can see, there is nothing wrong here: Since the properties of the material change where the green and the yellow parts meet, you do not have a single conductor but two different ones with ...
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### If electric field inside a conductor is always zero, then why do free electrons move?

Then how do free electrons move from atom to atom in random direction? The random movement of electrons in a conductor is thermal motion. It exists regardless of the presence of an electric field. ...
• 74.5k

### Why do electric field lines curve at the edges of a uniform electric field?

These are so-called edge effects. The straight electric field lines connecting two surfaces is a solution for the infinite charged plates. In practice, no plates are infinite: they have edges. Far ...
• 60.5k
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### Is electric field inside a conductor really always zero?

The "nothing left to move" scenario is impossible with a metal: the electrostatic potential needed to deplete a metal is far beyond what is sufficient to destroy any experiment. It is, ...
• 21.8k