103 votes

Why isn't the universe full of electrons?

I think this is a very creative question. You are thinking: There are so many atoms in the universe that all of their electron wavefunctions should overlap and lead to a detection everywhere. But ...
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  • 1,835
24 votes

Why isn't the universe full of electrons?

Let's suppose we are surrounded by an approximately uniform density of hydrogen atoms $\rho_h$, then the number of atoms in a shell around us of radius $r$ and thickness $dr$ is: $$ dN = \rho_h 4 \pi ...
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8 votes

Why isn't the universe full of electrons?

I think, you are underestimating the effect of the electrons' amplitudes exponential decay. While the wave function of a bound electron is indeed non-zero everywhere, the amplitude of the wave ...
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5 votes

How do electrons know where to "drop to" when returning from an excited state?

There's no restriction. An excited electron can drop from any state to any lower state. The full emission spectrum will therefore include lines that correspond to transitions to the $n = 1$ state, to ...
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5 votes
Accepted

How do electrons know where to "drop to" when returning from an excited state?

Scientists don't control the energy level where an electron lands. They observe different series based on what equipment they use to make the measurements. For example, if scientists only look at the ...
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  • 21.6k
4 votes

What is the shape of the path that electron makes in an atom?

While it is a useful concept for to use in the introduction to quantum mechanics, the planetary model of the atom is quite false. The electron is not a point like particle literally orbiting the ...
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  • 717
3 votes

Is a moving electret considered a current, and would spinning one make a magnet?

Moving an electret is not equivalent to current in a wire, as you say. However, it is current. The positive and negative poles of the electret are physically separated, so a moving electret ...
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  • 4,113
3 votes

What is a current?

It depends if you're asking about the nature of current, or about the way it's counted. About its nature: as @Dandan0101 said, it varies. It can be electrons in metals, electrons and holes in ...
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  • 2,256
2 votes

Can you measure an electrons spin in multiple ways before measuring its entangled partner?

If you start with an entangled Bell state like $\frac{1}{\sqrt2}(|{\uparrow}{\downarrow}\rangle + |{\downarrow}{\uparrow}\rangle)$, then after your first measurement along the vertical axis, the ...
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  • 17.5k
2 votes

What is the Feynman diagram associated with Bremsstrahlung?

Actually, the Feynman diagram for Bremsstrahlung is that of Compton scattering with the little difference that the incoming photon at the "first" vertex is a virtual one that is generated by ...
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2 votes

What is a current?

The fundamental definition of current is the flow of charge, regardless of what the charge carrier is. It happens that in most conductors, like the metals that the wires of a circuit are made out of, ...
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  • 2,067
2 votes
Accepted

Electrons carry the bulk of heat flux in the solar wind?

Electrons provide additional heating by carrying the bulk of the solar wind heat flux and through collisions with the protons. First, the solar wind is a weakly collisional plasma at best (e.g., see ...
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2 votes
Accepted

Potential Energy of an Electron inside a circuit

You cannot analyze an ideal wire connecting the terminals of an ideal battery, it is an irresistible force meeting an immovable object. In the case of an ideal wire connected to a real battery, the ...
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  • 65.8k
2 votes

Is a moving electret considered a current, and would spinning one make a magnet?

Any motion of electric charges is an electric current. That's the very definition of an electric current. Any electric current generates a magnetic field (see Biot and Savard law, or Maxwell-Ampère ...
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  • 2,256
1 vote

Is charge carrier density an intrinsic property of a material and is thus constant?

No, the carrier density will depend on the material, and for metals you might argue that it is a property of the material, but it will still depend on the details. If you look at it from a condensed ...
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  • 619
1 vote

How do experimentalists measure the exciton binding energy?

One can measure light absorption in a semiconductor. Peaks in absorption could appear corresponding to the photon -> exciton transition. They appear bellow optical gap
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