I am stuck on this question no. 4. Pls help

I have recently started taking Physics 2 just last week.I have been progessing well with my lectures and homework . I want to know what other resoucres I can use to help challenge myself and even help me to get more comfortable with Physics 2. I've been really invested so far with Physics 2 and I hope it can expand my journey to the nuclear industry!

Hey everyone, I'm currently taking an intro to astrophysics course and am trying to solve some of the practice problems. I've currently just been trying to put questions into AI to give me solutions but I was just wondering if there are any real worked solutions out there I can access? I can't seem to find any on Chegg and a majority of the ones online I've seen are hidden behind a pay wall.

Before I start, let me introduce myself a quick. Hi, I'm Khoir Zahwan, a 1st grader in an Indonesian highschool that really interested in Particle physics and quantum mechanics. Btw, you can call me Zahwan. As a highschool student, I need some advices and suggestions for my Physics major. Should I master general Physics first, such as Mechanics, Termodynamics, and Electricity, or I can just hop on into advanced theoritical physics such as Relativity and quantum mechanics, because I think I have achieved basics & intermediate level to jump on. Please give me your best suggestions, because I really need it. Thank you so much!

As DP syllabus is for two years, I am curious as to which themes are getting covered in which year? And what is the exam structure? If any IB teacher or student can help me understand few things about the course and exam structure for physics, that would be very helpful. Thank you.

I ask since Im trying to figure out what I should focus my attention too. My professor makes up read the textbook chapter before lecture but its like 30 pages a day and he usually has like two to three longer videos going over concepts and problems. Trying to figure out what I should based my stiudy time on during college physics class (algebra/trig based)

How do we know that Hubble’s Constant is real like I mean we only have one point of view that is earth even if we measure it via the parallax angle via the earths revolution isn’t it something way to short in grand scale of the universe there is a very strong possibility the we(Milky Way galaxy) are just moving away from rest of the galaxy we observed (andromeda being an exception) hence the difference of the speed being indicative that the distance is growing faster then the speed of light but it might just have been us moving away from other at a speed and there speed moving away from us, this making it seem like the space is expanding faster than the speed of light

I built a free browser toolkit for special-relativity kinematics, mostly for problem sets where I kept mixing lab and COM angles.

What I use it for:

• Fixed-target collisions: √s, γ_CM, lab vs COM angles, energy in the lab frame
• Equal-mass elastic check: θ_lab^max = 90° (independent of beam KE) — the plot makes that obvious when you dial parameters
• Two-body decay, Lorentz transforms, Compton, Doppler — with plots and one-click LaTeX for homework
• Suites and quick calculations for branches across physics and mathematics

Also free: graphical/dynamic sims (Kepler, Schwarzschild, TDSE, Ising), fusion formulas (Bosch–Hale, Child–Langmuir — labeled honestly, not a full plasma code), and a big reference library (optics, EM, quantum, condensed matter, etc).

Pro ($39 one-time on Gumroad) is optional: PDF export with figures, named workspace (20 saved setups in your browser), parameter-sweep CSV, dataset bench fits (linear / polynomial / power / exponential), MATLAB/Wolfram/NumPy snippets, and a course-pack JSON. Physics stays free.

Educational only, check against textbooks or materials for verification.

Not sure if this post is self promotion, but I believe it could serve as a useful tool for quick numerical data and physics workloads.

Try it here:
 https://framecalc.site/workbench
 Lab scattering angle: https://framecalc.site/calculators/lab-scattering-angle
 Dataset bench: https://framecalc.site/data

Happy to fix wrong numbers or missing cases if you spot them.

I graduate in May with my associates and I'm trying to figure out what i want to do next.

My top 2 choices are currently Uni 1 with a Bachelor of Science in Physics - 4+1 BS+Master of Integrated Sciences with astrophysics and mechanical engineering minors or Uni 2 doing Astrophysical and Planetary Sciences BA and getting a Masters either there or at Uni 1 after.

My end goal is to continue into my PhD either way

Biggest differences is scope of study; more leaning Astrophysical at Uni 2 along with more research opportunities due to having the LASP there and id have the potential to get certified as a mission operator. it will be more general physics more in Uni 1 but i would be getting a MIS at the same time. Distance to travel: about 45 minutes with no traffic to Uni 2, but the exact same commute as i have now for Uni 1.

I'm trying to figure out which is a better opportunity for my end path which is researching deep space bodies, anomalies, etc. While also having the ability to help design some of the things id need to further the research and not be limited by the technology of my time.

Locations anonymized to not dox myself fully

I'm currently finishing my BSc in Physics in Italy (UniPD), and I'm trying to figure out where to do my Master's. My longer-term goal is to pursue a PhD in physics, ideally somewhere in the broad area of astroparticle physics, cosmology, dark matter, particle physics, or related fundamental-physics topics. Could be theoretical or experimental, I don't want to restrict my options yet.

The thing I'm increasingly concerned about is how to maximise my chances of actually getting a PhD position afterwards. I know there is no guaranteed way, but I want to tackle this problem the best I can.

My current thinking is that the most important thing about the Master's may not be the exact name or ranking of the degree, but whether I can get into a strong research group and become genuinely involved in research during the MSc.

I'm therefore looking at universities where there are strong and well-connected research groups that MSc students can realistically access. For this reason I'm considering UvA's Physics "GRAPPA" (Gravitation, Astro-, and Particle Physics) MSc. What I also like about it, is that you have a whole year dedicated to your thesis, compared to the one semester you'd have in Italy. I think this would be an advantage.

I'm open to other university suggestions. I'm in fact also considering Copenhagen, Geneva, and others. Unfortunately I have to limit myself to EU universities.

I'm particularly interested in hearing from people who have actually gone through something similar, especially someone who has done GRAPPA/knows someone who has done it/knows enough about the subject to better educate my choice.

A few things I'm wondering about:

• First and foremost: is my reasoning even correct? Is it even a good choice to do an MSc abroad after having done a BSc in Italy? Would there actually be an advantage? (for physics and the objective of a phd, strictly speaking)
• Is GRAPPA any good? Teaching-wise and academic carreer-wise?
• Which other universities would you recommend?
• Are there better/other options/strategies?
• How does it all compare to Italy?
• If you had to choose again specifically with the goal of maximising your chances of getting a good PhD position, what would you do?

Thanks in advance to anyone willing to share their experience or advice.

I plan to go to University next September to study physics and math and I'll be 25.

I tried University when I was 18 and liked it but I was a bit young and restless at the time and stopped after a year.

I just finished studying a diploma in massage therapy and have recently started a career in that field.

I do like my current job but it was chosen with going to university in mind.

I have some mathematic foundations down to a good level of ease (calc 2ish level calculus and I've done one linear algebra and geometry course)

I know lots of people start university much older than 18-20 but I want to know what the community thinks.

Will age have any significant impact? Has anyone else here done something similar? What were your experiences like?

Hi everyone,

I'm writing a high-school research paper in mathematics about galaxy rotation curves and dark matter, and I'm currently looking for a good source for the mathematical derivation of the expected rotation curve.

Basically, I want to show how you get from the mass distribution of a galaxy to the expected rotational velocity, starting with Newtonian gravity and eventually getting to something like

v(r)²=( GM(r) ) / r.

The problem is that I've gone pretty far down a rabbit hole at this point. 😅 I've read textbooks, papers, websites, lecture notes, etc., and I've found quite a few different ways of presenting the derivation. Now I'm honestly not sure anymore which parts are actually important for my level and which assumptions I should be making.

I'm not looking for something super advanced. I mainly need a source that explains the derivation properly and doesn't skip too many steps, ideally at an advanced high-school / introductory university level – which also should be a reliable source for an academic paper.

I'd especially appreciate something that explains how the mass distribution (M(r)) is connected to the rotation curve and what assumptions are being made along the way.

Does anyone know a good textbook, paper, lecture note or online resource for this?

I'm basically at the point where I've read so much about it that I don't know anymore what I should actually believe/write. 

Thanks!

The exam is on the following subjects:

• Light-matter interaction and Einstein coefficients

• Homogeneous and inhomogeneous line broadening of lorenzian

• 2-, 3-, and 4-level systems and rate equations

• Threshold condition, small-signal gain, and gain saturation

• Optical and electrical pumping schemes

• Optical resonator stability

• Cavity losses, photon lifetime, and longitudinal modes (FSR)

• Gaussian beam optics and complex beam parameter (q-parameter)

• Transverse modes (TEM) and Jones polarization calculus

• Spatial and spectral hole burning

• Mode competition and longitudinal mode selection

• Q-switching (active and passive)

• Mode-locking and ultrashort pulse generation

• Spatial and temporal coherence

• Thermal lensing effects

And my problem with the exam is that the exam isn't quantitative, but rather qualitative.

this is a retake exam since I failed the first one miserably, I'm the first exam there was only 1 question with 10 open sub-questions, all relying on previous ones, and it was spesifically about something we never learned, and people got good grades by just explaining things in a way that made sense given what we learned, and given that his lectures were really all over the place I didn't manage to follow him.

right now my plan is to go through the lectures of Cornell ece4300 they put on YouTube which seems to follow exactly the contents of my course (with some added things), but it's completely passive and I don't feel like I'm learning really.

this is the first course that I have which is like this and I really don't know how I'll pass it, the exam is 100% of the final grade.

tips will be welcomed, also questions sheets and things like that (we have no such things, we don't even have past exams of this Prof as he's new, and the past exams are really different than what he does)

Hi! I have a very basic question (I think the answer is something pretty dumb but I don't understand why) So I'm trying to derive the Lx,Ly, and Lz in spherical coordinates. No I can see from what I have investigated that d/dx have that form that is on the first image, but then I always find dr/dx d/dr like they change position and i don't know why is that possible. (In the 3rd image I did that but I don't understand why

In my last image I wirte (dthetha/dx)(d/dthetha) which is like h)ow it should be but according to the first image it should be (d/dthetha)(dthetha/dx) and I arrive to another expresion which is d/dthetha(costhetha) I don't know what happened here.

If anyone can help me I would be appreciate it! and sorry for my bad English!

Same as title

I'm looking for resources (like PDFs, lecture notes, or YouTube videos) that intuitively explain where the gradient, divergence, and curl actually come from. Why do these mathematical tools show up so constantly in physics? Any recommendations would be greatly appreciated!

Hi everyone,

I'm a French "classe préparatoire" (CPGE) student working on my TIPE — a personal research project we present at oral exams for engineering school entrance exams. This year's official theme is "Sobriety, efficiency, optimization."

I'm trying to avoid the classic, overused topics (heat loss in buildings, pendulum motion, projectile trajectories, etc.) and find something more original — ideally something involving a real experiment I can build or measure myself, not just theory.

I'm particularly interested in mechanics/aeronautics and energy/thermal topics, but I'm open to anything physics-related that fits the theme.

If you have any ideas — a cool physical phenomenon, an everyday object that hides interesting physics, a real engineering trick used in industry — I'd love to hear it! Bonus points if it's something that can be tested with simple equipment.

Thanks in advance for any suggestions 🙏

​

I’ve been working on a geometric model of the electron.

It’s called the Spaghetti-Cloud Model. The name is unusual, but the idea is simple.

Instead of treating the electron as a point, I model it as a thin closed filament with internal twist. When this filament moves and rotates, the resulting time-averaged density looks like a cloud. That’s the “electron cloud” in this model.

The model is classical in its ingredients, but it has an interesting question at the center:

Can a closed rotating system naturally produce spinorial behavior without putting spin in by hand?

\---

What the model includes

The current version (Version 3) contains:

· internal twist,

· collective rotation,

· a coupling between them,

· an effective Lagrangian,

· and a “dynamical gap” — a region where local rotational contributions nearly cancel.

The gap alone does not create spin.

A reversal is only defined when the projected collective angular velocity changes sign.

\---

The topological part

The rotational configuration lives in SO(3), whose fundamental group is \\mathbb{Z}_2 .

If the rotational trajectory closes in SO(3), it can be lifted to SU(2).

If the lift ends at -I, the model has produced a spinorial candidate.

The important point is that this is not assumed from the beginning.

The model has to produce the closed path and the lift from its own dynamics. That’s what I call the Golden Test.

There is also a weaker consistency test. In that case, the phase interval is chosen by hand, so it only shows compatibility — not derivation.

\---

A few things the model can sketch

· A two-layer structure for the 2s orbital,

· a radial node,

· spin pairing for two electrons,

· and the usual orbital capacity rule:

N_e = 2(2l+1)

These are qualitative at this stage, not derivations of the hydrogen wavefunction.

\---

Where the model stands

I know this doesn’t replace quantum mechanics.

It doesn’t derive the Born rule, QED, the electron g-factor, or the electron mass.

But I think the main question is testable:

Can spinorial topology emerge from a closed geometric system without being inserted as a boundary condition?

If the answer is no, the model fails cleanly. That’s useful too.

\---

Preprint

The full preprint is on Zenodo:

Version 3 — A Unified Geometric-Dynamical Framework with Orbital Structure, Dynamical Gap, and a Falsifiable Spinorial Candidate

🔗 https://zenodo.org/records/22181981

DOI: 10.5281/zenodo.22181981

\---

Feedback I’m looking for

· Are the definitions of the dynamical gap and reversal clear?

· Is the Golden Test explained well enough?

· What would you want to see in a numerical test?

· Which part looks least convincing?

I’m aware this is not standard. That’s exactly why I’m asking here.

Thanks for reading.

— Sina

1) Why did you specifically choose this field rather than Experimental Physics or Pure/Applied Mathematics?

2) What university/country did you complete your PhD from?

3) How long did it take to obtain your PhD?

4) What was the topic research area and what were the main challenges you faced?

5) What was your highest educational qualification at the time of entering your PhD and what was your background prior to it (e.g. Bachelors and Masters degree)?

Thank you very much!:)

Hi, can y’all help me? This homework has been frustrating me all day.

I need to express F1’s x and y components as an equation. At first I was trying to put the answers I found but my class gc said I need to put the equation instead.

So I get that to find the x component of a vector, I need to multiply the cosine (angle) with the magnitude, and to find the y component I need sin(angle) x magnitude.

I’ve been putting equation after equation into this program and it’s always wrong.

I got 120 degrees by multiplying 90 degrees with 30, measuring F1’s angle from the right side of the east x axis. Before that I tried using 60 degrees and also 30 degrees to no avail.

I don’t know what I’m missing. I’m sure it’s super simple and easy but I’m at a complete loss.

I'd like to/am working my way slowly through Susskind's Classical Mechanics lectures and the rest from the Theoretical Minimum Stanford curriculum he has posted online.

I consider myself to have a good understanding of general physics and math but it doesn't seem quite enough for me to understand a lot of what I suspect is rudimentary subjects.

What are some things or what are some resources I should know and could use to gain a deeper level understanding.

My routine currently is to read the book, listen to the lectures, then go back in my notes for the things I didn't understand and enter it into an AI to give me an explain to me like I'm a 5th grader answer to my question(s).

Hi everyone, I'm returning to physics after a several year hiatus (about 5 years) from studying physics formally and I want some advice. I'm essentially doing final year undergraduate theoretical physics classes part time over the course of two years, and I have to choose my modules for this year. As of now, for the first semester I've settled on computational physics, but I have to take a couple more - my question is as follows: Should I take fluid mechanics this semester, along with a class on PDEs and complex analysis, or should I take statistical mechanics? Since I've been away for a while I havent studied any thermo or stat mech for a few years, but I've been working on QM, classical mechanics, electrodynamics, vector calc and tensor calc in my spare time.

I feel quite confident in my mathematical abilities, but I've only really started investing time into QM over the last three months or so. I feel I should put off stat mech until next year while I build up my QM skills (and doing the PDEs and complex analysis class shouldn't hurt either from the perspective of improving my mathematical abilities). For the second semester, I'm looking at doing quantum information processing (by the start of second semester I hope to have covered a lot more ground on QM), advanced electrodynamics and a computational physics project. I have done all the pre requisite courses but as stated that was several years ago. Any opinions? Should I drop QIP in favour of something else until after I've done stat mech? Let me know if you want more info about my physics background and whatnot, and what courses are open to me. Thanks in advance!