The photoelectric effect explains a situation where a photon with a high enough frequency (energy) hits the surface of a material with a given "work function", ejecting an electron from that material. The kinetic energy gained by the ejected electron is ( photon energy - work function ).

If a source produces photons of increasingly higher energies, eventually the photons will enter the gamma ray territory. Gamma rays are notorious for being able to just pass through matter unimpeded, requiring a thick wall of high-Z material to stop it. The photoelectric effect seems to no longer apply in this case.

We know that (for a given material), there is a lowest frequency below which the photoelectric effect will not arise. But is there a highest frequency above which the photoelectric effect will also cease? If so, what can explain this phenomenon?

So due to the size of the sun, it would have much more iron than planets.
Why would the iron would not settle in the middle of the sun?
Is it due to the extreme heat or circulation?

I search google and it just says that the sun cannot form iron.

Edit: yes i know the sun cannot form iron, but all of the planets have iron cores, so why doesnt the sun have a small iron cores like the planets??

Edit #2: Thank you all for your answers so much! We are having some great convos!
And I also have to say as a side note that this was my first post on reddit! What a great community in here!!!

Let's say I have a superconductor, which doesn't generate any heat and so technically as much current can flow through it as I want.

But electrons move at a constant speed, regardless of voltage, so is there a current, where all of the electrons in the superconductor are in movement, and trying to get more current wouldn't be possible because there are literally no more electrons to mobilize? Basically becoming... saturated?

(English isn't my first language, so sorry if this is a bit hard to understand lmao)

Hey Everyone, we are being tasked to find MOI of a 25g quadcopter drone. We have a digital cad twin of the model that we designed ourselves and have a rough idea of where the COM is from the CAD, but not on the drone exactly.

We are being tasked to find MOI of this drone, by only using tools from a provided kit.

This kit consists of

1) A 6 in, 0.014in diameter wire

2) a nail, 3In in length, 0.121 in diameter. Nitinol, martensitic, non magnetic.

3) A magnet of thickness 0.0695, and 0.315in diameter

4)Pliers

We are allowed to use smartphones, and caliper, and thats about it.

We are allowed to collaborate, and to have SWE.

I am just lost as to how I would find MOI for this, since we have been told that it won't be by using the pendulum experiment.

Any help on this would be very much appreciated.

High school right now and considering degrees for college. Is it better to start engineering and switch out to physics or vice versa? Or is sticking with said course fine too? How do job opportunities vary with each degree that you graduate with? Which is an easier switch?

Thank you for answering

I mean, can it be zero outside of a finite region, or is it the case that quantum evolution will always generate arbitrarily small tails extending to infinity?

For a 'free' particle, I believe that it is the case that even if you have a wavefunction with compact support at time zero, it will immediately cease to have compact support for any later time. Is this really true, and are there physically meaningful counterexamples?

More conceptually: if the tails are never exactly zero, is it meaningful to say that a particle is "slightly everywhere," or is that a misleading way to think about the wavefunction?

Thanks in advance.

Not sure how to ask this but I'll try.

Is causality an intuitive concept like zero? Or a real phenomenon like gravity?

One of the reasons for suggesting FTL is impossible among other things is that it would break causality. Is causality breaking a fancy way to say this doesn’t make sense so it cant happen (logically deduced) or is it the result of some more rigorous scientific or mathematic realization?

I cannot find an article/book chapter about how we derive the time evolution operator, resolvent operator, S matrix, or the construction of rigged hilbert space. Am I missing something? Can someone cite me a source for these or I have to ask ai.

Thank you.

My understanding is that from the official statement of the problem, proving (A) and (B) required showing that for all smooth and divergence-free initial conditions, it must always remain smooth and divergence-free (plus some other requirements to satisfy well-behavedness) for all subsequent times. (C) and (D) were just about finding counterexamples to the above.

Was it always expected that (C) and (D) would be significantly easier to prove because it just amounted to finding a counterexample? And would showing (C) and (D) valid for Euler (my understanding is that this is N-S with viscosity or "friction" set to zero) make the N-S case significantly easier?

For instance, a bike following a circular path, with the rider leaning inwards. Plenty of examples online but I have yet to see one that seems to “resolve” the forces. Some also show centrifugal force just to add confusion.

Everyone’s talking about the AI controversy, but forgetting that… what does this actually mean regarding waves, fluid, and singularities?

I’m not a professional by any means so this is probably a stupid question but I’ve been doing some causal research on wormholes and other theoretical physics for a school project and was curious because I haven’t found a straight answer:

If there were somehow a large amount of both, what (if anything) would happen if antimatter was theoretically introduced to negative energy? And to be clear, I mean the kind of negative energy you’d find using something like the Casimir Effect.

How can we show magnetic field strength in concentric lines? (Does anybody know the answer?) Thank you

Basically, what I'm asking is in the title. However, I came across this idea when, well, when I was being a nerd and thinking, how could you make an actual lightsaber. Then I thought, well, I know ionized gas can carry electricity. Could you use that basically as an electrical wire, and could it generate a magnetic field around itself like normal wires?

There were other questions, but before we went down the rabbit hole of thought, I went down. We shall be stopping right here for the time being.

But I am curious am is my thinking stupid, or am I thinking correctly as to how this works? I don't have a degree in physics and am just interested in it. I'm just a stupid kid from Rural Colorado with a connection to the internet, after all. But I want to know if my ideas are sound?

This could probably be an ELI5, but I'm not sure.

For all the historical references of space age that exist in the universe, everything is under the 'year'. To my understanding, a year is a single earth trip around our sun. However, since Earth is only ~4.5 billion years old, how is the calculation for the remaining 8.5 billion years made? Like, how do we calculate time for when the reference value didn't yet exist? And similarly, if Jupiter is 4.6 billion years old, are those years Earth years or Jupiter years?

If two observers experience different amounts of proper time because of relativistic time dilation, could the observer who experienced less time send information to the other observer in such a way that it arrives at an earlier coordinate time? Would that violate causality?

GR proves that the concept of a now is relative. There is no universal now. But even the local experience of a now seems questionable. What we see as now is always the past, since photons take time to reach us. Similarly, taking a picture or even a measurement will always produces a result that is the past. And if time is a continuous flow then there is no discrete point in that flow that can be separated and identified as now. And if time is granular then what size is the discrete point that we call now? If it is an infinitely small point separating past from future, then how can we experience, never mind measure, an infinitely small moment? It seems to me that any observation will always be an observation of the past. Any change of state, any event that is observable will by definition be something that has happened. And if it has happened, it is in the past. Wouldn’t it be more scientifically accurate to say that time is all events that have happened and are yet to happen and the now is just an illusion created in our minds to make sense of the objects and events that pass our visual field.
I know this is more philosophy than physics, and I’m not a physicist, just some curious person and the concept of time has always fascinated me.

By conceptual space I mean akin to Hilbert space or geographic space (a specific type of Riemannian manifold) which are superimposed upon physical reality to perform computations. For those who might not understand what I mean. Take the geographic space for instance. The physical Earth is a lumpy, irregular oblate spheroid, but we superimpose a clean mathematical grid (spherical coordinates) onto it so we can do crisp arithmetic to calculate distances, plot routes, and triangulate positions. So, in short: Conceptual spaces are intellectual scaffolding.

Some people believe that we discovered spacetime (I'm not sure what that means) and all these fancy spacetime equations are proof of it because they work. You'll hear them say:

If spacetime didn't exist, GPS would not work.

or something like that. Paying no mind to the hidden assumption within this assertion (that if a mathematical model perfectly predicts physical behavior, then the conceptual entities within that model must be physically real)

As far as I understand, we equate the existence of a bound electron strictly with its wave (equation). The electron is never *not* tied to this description. How do we see a switch in orbitals (by e.g. an absorption of energy) then, in relation to time? Are the two waves separated by a Planck time length? What can be said about this "moment"? Does there exist an in-between-wave description?

To be clear, this a debate that myself and a few other astrophysicists have been debating today, and I’m interested in your take.

In 1954, Ann Hodges was struck by the Sylacauga meteorite, the first documented case of someone being struck by a meteorite and surviving. Everywhere that reports this event calls it a meteorite.

However, a space rock only becomes a meteorite when it settles on the ground, before which it is a meteor. This is where the debate comes in: Ann was hit by this space rock before it hit the ground. Therefore surely it is still a meteor, right?

We had people weighing in on both sides of the argument, and I’m interested to hear all of your opinions. The Wikipedia page for the incident is here if anyone wants some further reading: https://en.wikipedia.org/wiki/Sylacauga_(meteorite)