New answers tagged

0

Matter can very accurately be described as a collection of electrons, protons and neutrons, gathering into heavier stuff like atoms. Whittling down matter will just end up in a bunch of disconnected electrons, protons and neutrons. A "chunk of matter" at that point would indeed just be some combination of a few of these particles. Thus, if it had ...


1

One kilogram contains 9*10^16 Joules. Lifting a kilogram, or 9*10^16 Joules, 1000 meters takes 10 kJ. So it looks like 1/9000000000000 of energy is lost when transmitting it from sea level to 1000m above sea level. Here "lost" means "converted to potential energy".


1

I interpret the question as "Is a charged battery battery heavier than a discharge one?". A modern battery easily holds 0.4 MJ/kg, corresponding to a mass of 0.44 10$^{-11}$ kg/kg by the famous relation $E=mc^2$. So a fully charged battery weighs 4.4 trillionth more than an empty one.


0

If you are using alternating current there is no loss since there is no net flow up. If it is a direct current gravitation acts as if there was a voltage resisting the flow up (and enhancing it down) corresponding to $m_e g/q\approx 5.6\cdot 10^{-11}$ V/m. This is exceedingly small. In a general relativity framework there would be a gravitational time ...


1

It does not, for two reasons. First, for every electron that you push uphill through the wire, another electron flows back downhill in the return wire and any work expended in lifting the one electron is returned by the electron that is coasting downhill. Second, even if this were not true, the gravitational force is fundamentally smaller than the ...


2

Balmer absorption arises from the $n=2$ level. To have a significant occupation of the $n=2$ level it has to be quite hot, because of the 10.2 eV gap between the ground state and $n=2$. The fraction of atoms in the $n=2$ level just grows with temperature. But at the same time, the ratio of hydrogen atoms to hydrogen ions decreases because more hydrogen is ...


1

... we only use magnets to redirect the electron via the Lorentz force back into the capacitor. The path that the electron follows is not a circle. As you may remember, the deflection of the photon is an acceleration, and every acceleration of an electron is accompanied by the emission of photons. The recoil of the emitted photons takes some kinetic energy ...


2

More subtle than it looks... The electric field (lines of force) is not confined to the gap between the plates. It spreads out sideways. So during the dashed-green part of the trajectory the electron feels not only the Lorentz force from the magnetic field but also a decelerating electric field. Yes, as you get away from the capacitor plates the electric ...


3

There is sound evidence that no fourth physical dimension exists in this way. If it did, stuff would linger in there and many conservation laws, of mass, energy, charge, etc. would appear to be violated in our 3D world. Also, the jump of say an electron is thought to be instantaneous. There is no measurable time delay. If a classical particle were to travel ...


2

As far as anyone knows, the charge is a fundamental property of the electron, with no deeper explanation. One thing that is curious is that the charges of quarks come in exactly 1/3 or 2/3 fractions of the charge of the electron. This implies, among other things, that atoms are exactly neutral. A priori, there is no reason for these quantities to be related. ...


3

The simple explanation is that we only need to consider magnitudes in the equations, as directions are trivial in this situation (there is only one force, and it is clearly in the required direction). Now think of $F_e$ and $F_c$ not as forces, but as magnitudes of forces. This is consistent with the lack of vector notation.


0

The force equation says -Fe + Fc = 0. So you do have a negative sign coming from the negative charge of electron.


0

A permanent magnet actually has angular momentum. As it is electron angular momentum, mostly spin, the crystal itself does not rotate. A iron magnet, for example, has 5/2h of spin angular moment per iron atom. For 1 mole of iron it is 10$^{-9}$ Nms of AM. If the magnetic order disappears this will be converted into crystal AM. This is a small amount but ...


-3

The magnetic moment could be the sum of that from many small rotating or revolving charges. Then the magnet as a whole doesn't have to rotate. It could be atoms spinning inside crystals. It could be electrons spinning around atomic nuclei. It could be electrons spinning like tops. We can make up lots of stories to explain it. I'm not clear how to tell ...


0

If I'm interpreting this question correctly, I think this is actually a great question which does, in fact, have a definite answer. Essentially it seems like you're looking at the properties of fundamental particles and wondering why they seem so arbitrary. Spin stands out, as compared to mass or charge, I think because spin is an exact number with no error ...


0

The relationship would be very similar. The only difference is that you have to consider the conservation of the 4-momentum instead of the classical conservation of energy. Note that in order to have a relativistic outcoming electron the energy of the incoming photon has to be in order of $\sim 30 keV$. This means that those photons are in the range of X-...


0

Newton's laws do apply. The overall system will not rotate. While the electrons are rotating in one direction, the rest of the gear will indeed be rotating imperceptibly slowly in the other. But the rotation is constant, as the propulsive EMF is being exactly opposed by collision forces between electrons and metal atoms. I would suggest that these collisions ...


1

This is an excellent question. I asked it myself (not for the first time) when I saw a picture of the Crookes tube, and did some research. The key thing is to remember that the cathode ray tube evolved out of the discharge tube. This is a tube with an anode and a cathode, filled with a gas (e.g. Neon) at low pressure. A potential difference of several ...


1

Electron releases the work function energy to be bound to metals again.


4

In that case the electron absorbs the energy of the incident photon (which will be greater than the amount of the work function). So the energy after this interaction would be contained in the scattered electron. So $$E_{\gamma} = K_e + \phi$$ where $E_{\gamma}$ is the energy of the incident photon, $K_e$ is the kinetic energy of the ejected electron and $\...


1

There's probably no one answer to this because despite their similar names, the two kinds of devices work on substantially different principles. But consider a couple of factors: Multiplication process: In the PMT, the electrons colliding with each dynode must have enough energy to overcome the work function of the metal and break additional electrons out ...


15

The electron is defined in the Standard Model as a elementary particle, pointlike, with no size or spatial extension. Protons and neutrons that make up the nucleus are on the other hand composite particles as defined in the Standard Model, and they do have spatial extension. Of course, these are made up of quarks, antiquarks, and gluons, (contrary to popular ...


2

The number at the bottom left is the charge (measured in multiples of the elementary charge). For a nucleus this charge is equal to the number of protons ( each having charge $+1$) or the atomic number. For an electron the charge is just $-1$.


25

The question confuses the electron "cloud", which is really the probability for where an electron may be found, with the size of an electron. The electron is sizeless, which can either be taken to mean that it has zero size, or that size in the quantum domain is a meaningless quantity, depending on how one chooses to think of it. An electron has ...


7

"from quantum mechanics we know the electron is really a non-localised elecron cloud" This is not correct. The electron is a point particle and smaller than a nucleon. A quantum particle should not be confused with a quantum wave function.


0

The repulsion of 2 electrons is described in the form of exchange of photons(same spin). When the electrons exchange a photon they scatter. A more detailed explanation is given by a Feinmann diagram. The energy of each photon and electron are proportional to the Planck constant so their energy can never be infinite. Also if the 2 electrons get really close ...


4

Your guess is within classical mechanics, but electrons are elementary quantum mechanical point (not fuzzy) particles and when the dimensions are commensurate with Plancks constant , classical estimates of its behavior no longer work, and quantum mechanics takes over. In quantum mechanics two electrons interact with specific rules and once the energy of ...


Top 50 recent answers are included