Physical Definition and 1000 Threads

This isn't a homework question per se but it's a question that I had while reading through my textbook so I think it's appropriate here. I just started studying Quantum Mechanics and so am getting familiarized with the meaning of wave functions and their behavior. One question I can't seem to...

Homework Statement The problem asked us to show that the Euler-Lagrange's equations are invariant under a point transformation q_{i}=q_{i}(s_{1},...,s_{n},t), i=1...n. Give a physical interpretation. Homework Equations \frac{d}{dt}(\frac{\partial L}{\partial \dot{s_{j}}})=\frac{\partial...

How did scientists/chemists experimentally determine how many electrons an atom has? Hydrogen, carbon, oxygen, etc... I'm wandering what physical experiment would tell you how many electrons an atom has?

In another thread, which I don't want to derail, the issue came up as to whether or not the event horizon of a black hole is physical. Some contend that it is physical but I contend that it is merely a set of coordinates (most easily represented by the spherical coordinate R). I DO...

This a general, layman question. Computer processors work with binary digits, 1 and 0. Of course, computer processors can be seen as microscopic forms of Babbage's analytic engine. So in reality, in the circuits of a microprocessor, what physical form do binary digits take?

Hi All, I was in a process of processing my vibration-test data. I now generated a plot of the autocorrelation function of the object acceleration. Please see the attachements (the second attachment is the close-up for small tau's). The x-axis in the plot is the time delay tau. You can see...

Homework Statement I have a physical pendulum that is rotating about an fixed axis. The period is: T=2\pi \sqrt{\frac{I}{mgd}} I = moment of inertia d = distance between the center of mass and the axis. The problem is: If you add a mass in the end of the pendulum. The period is going...

I am curious what the nonlinear bernoulli equation is used to model. Is there a certain topic or context where it shows up often? Can any suggest some references for more info? I am reviewing some ODE stuff for an upcoming exam and would really like an intuitive feel for the equation and its...

I've read that gauge invariance leads to a fundamental phenomenon.What is that? Thanks

In SR, pure relative velocity between two observers causes a time dilation between them. It seems that if the two observers were at rest w.r.t. each other at some point in time, then the one who accelerates to achieve the relative velocity is the one who gets time dilation (i.e. comparatively...

lens -- What physical features makes a lens thin? What physical features makes a lens thin? How can you differentiate one lens from the other based on their thickness? What is the measure of their thickness?

What is the physical significance of Refractive Index(RI) ?

Hey guys, I hope this is the right spot to this. I don't want to get another infraction. I just got recently got out of my first physical chemistry class and am now thinking towards the second one. I'm wondering which book would be the best supplement to read over the break and help me get...

Homework Statement A uniform metal disk (M = 9.81 kg, R = 8.99 m) is free to oscillate as a physical pendulum about an axis through the edge. Find T, the period for small oscillations. Homework Equations I (uniform disk, with axis through center of mass) = (1/2)MR^2 T = 2π√(I/mgd)...

I'm learning scattering theory from Griffiths' book, and I don't really understand the meaning of differential cross section; it's one of those things that I find hard to conceptualize and give a physical meaning to. The most intuitive description he gives is "the proportionality factor between...

For example, dividing by 2, means we cut something in two. But dividing by 0.5, can only be explained with multiplying something by 2. So, is there a "physical" explanation of dividing by 0.5? Is it "I divide by an entity that internally multiplies' or something as so bizarre?

In my intro. to GR class we recently covered the Kruskal Szekeres diagram and trajectories within the diagram. My question comes from a comment made by my professor about time-like trajectories emerging from v=0 and that if an emitter sends a light signal to an observer it will be blue shifted...

Homework Statement The invariance of physical laws to a coordinate change suggests a symmetry group structure. Can the operations of cordinate transformation be written as group operations? What is the group? Homework Equations The Attempt at a Solution At the moment I do not...

Hi, my question is, if there is an interpretation for electromagnetic gauge fields, whose components are imaginary. This would lead to an imaginary magnetic field... Does anything like this exist? Or is it forbidden ny some first principal arguments? Thank you in advance for every input! Melvin

Homework Statement Consider fluorescence (light emission from an electronically excited state of a molecule) in the presence of a quenching molecule M. Quenching refers to the removal of energy from an excited electronic state by collision, and so without light emission. A mechanism for such...

Hi all. I've been trying to study microwave and electromagnetic engineering . I'm not sure how I should interpret j in some of the field equations. For example, for the field equations for a rectangular waveguide resonant cavity are: E_{y} = E_{0} sin\frac{\pi x }{a} sin \frac{l \pi z}{a}...

But high frequency are absorbed, like gamma rays. I would think it would be the opposite. So what's the physical reason?

hi whats's the physical meaning of curl? and why it is a vector? it's definition is line integral per volume. i can't understand why this is a vector.

Hello, Please excuse me if the following questions are very mundane: (1) The Einstein tensor in indices form: Guv=Ruv-1/2guvR Does uv means the indices i.e. just as we define row column in a matrix.? (2) The Einstein tensor is symmetric. Does that mean in matrix as we mean aij=aji...

I have idea of physical signif of var(x),cov(x) but can't get derivations of equation. Hi all, I understood the facts that variance indicate the spread in random variable and covariance shows correlation between 2 r.v s etc. But I cannot imagine how we are arriving at their...

Not much else to say other than the title. In the Schwarzschild spacetime, the radial coordinate r didn't represent radial distance, but it at least represented the thing that determines the area of a sphere centered on the large mass. It doesn't seem like that interpretation can be given to the...

Is it agreed among the experts that physical matter as observed in nature and generally also space and time(classicality) have the properties they do, only because of the low energy limit that they have now(as opposed to the immense mass, gravity and energy density at the BB or a black hole)? As...

Coupled physical pendulums (URGENT) Imagine that you have coupled physical pendulums like this (see image below). mass is in the inferior part of the pendulum.* Now we let the right pendulum swing without initial speed = 0 with a certain amplitude. As we know, the amplitude of the right...

Let me know if i am correct here. Temperature is just the amount of energy associated with that particle or molecule? So why does that determine if it is solid, liquid, or gas? Why doesn't water turn into ice at room temperature when you compress it into itself enough? Like in star wars when...

This is a paradox that has been bothering me since I was taking algebra in high school. Let's say that I want to represent the distance between to objects. Given that numbers are infinite in both directions, by which I mean that there is no limit to how large, or small a number can be, there...

Hi All PF Members... I'm New to this website.. Also new to physics... nd I'm very exited about this aweSome website...where I can post my problems... Experts I want list of All physical quantities and their Dimension... I've been searching and cannot find any thing good enough... Sorry for my...

23.7 g of water is in a container of 23.7 L at 298.15 . The vapor pressure of water at this temperature is 23.76 Torr. A) What phases are present? B) At what volume would only the gas phase be present? C) At what volume would only the liquid phase be present? A) I know that only the...

Homework Statement Two balls, one soaked in concentrated HCl and the other in NH4OH are placed at the left and right ends of a 1m long evacuated glass tube, respectively. HCl and ammonia vaporize and travel down the tube, reacting to form a white ring where they meet. Where does the ring form...

Hello all, This is a homework problem for my CHE345 class. Not sure what to do here, please at least let me know if I'm in the right ballpark. Homework Statement A student decomposes KCLO3 and collects 35.2 cm^3 of O2 over water at 23.0°C. The laboratory barometer reads 751 Torr. The...

Can anyone tell me a self teaching book or lecture notes on physical optics which has all the concept written in very clear and simple way with lots of example and all the related derivation done in step by step manner . As I am not so familiar with this subject but I want to start it so a good...

Homework Statement I've attached a picture from a passage of my book (Liboff, Quantum Mechanics) with which I am having difficulty. Specifically, equation 1.25 claims to possesses a certripetal force factor (in the text underneith) and a moment arm factor. I see both of these terms present...

Is it a good idea to take P Chem without taking any chemistry at college level? My high school had a strong chemistry program (we did organic in high school) but I haven't done any Chemistry in college. I am currently taking Quantum Mech 2, and will be taking Thermal Physics and Condensed Matter...

Uh, my program is Biotechnology/biochem (might change it). I can take a "Biophysical chemistry"or a "physical chemistry" mind you, I am strugging to even pas year one physics i hate it and it sucks. So I really want something with not as much math. Does anyone know if biophysicalchem has less...

If you travel at a sufficiently fast speed, then according to relativity, you will age at a slower rate compared to your slower moving contemporaries. This implies that biological functions (say, of a person) and mechanical functions (say, of a machine) are literally functioning at a slower...

Homework Statement The equilibrium concentration of oxygen in fresh water exposed to the atmosphere is given for two temperatures. At 15 degrees celcius equilib [O2]= 630μmol/L at 25 degrees celcius equiln [O2]= 517μmol/L The expression for the equilibrium constant, K, between the oxygen...

I was trying to drink a vegetable smoothie, which I really don't like, and I vomited twice in the process. My friend drinks it without issue. What's the difference here? My conscious mind really wants to drink the smoothie, but a few gulps in I feel an uncontrollable gagging. I'm curious how...

Homework Statement This is actually a part of my physics lab assignment, but there isn't any physics involved here, so I chose to post this here. I hope that isn't a problem. Anyway, I've been given three data tables, and have been asked to make graphs for each of the data tables by hand...

Hello! I'm a math student, currently trying to write my diploma thesis. My field of study is complex dynamics (iteration of holomorphic/meromorphic functions, Julia sets and stuff). It's a farfetched idea, but currently I'm curious about a potential physical interpretation of the things I'm...

A mole of air (80% Nitrogen, and 20% Oxygen by volume) at 298.15K is brought into contact with liquid water which has a vapor pressure of 3168 Pa at this temperature. a) what is the volume of the dry air if the pressure is 1 bar? b) what is the final volume of the air saturated with...

Homework Statement The following data were obtained for trace elemental zinc in a particular sample of high purity (%Au> 99.99%). The results are given in mg Zn/ kg Au. 15.38, 15.17, 15.33, 14.88, 14.71, 15.42, 15.60, 15.22 Find the zinc content and the uncertainty at 95% confidence...

I was watching a video on string theory and they claim that its all vibrating strands of energy. I thought energy was just a property of the system, not a physical entity. So do they mean something else by "energy"?

Number 1 For the gas phase reaction, cyclopentene + I2 = cyclopentadiene + 2HI, we find that ln Kp = 7.55 - (4817K / T) (where the symbol K on the right hand side refers to the units Kelvin). What are the changes in entropy and enthalpy? Possible answers are ΔSo = 40.05 kJK-1mol-1 and...

hello! there is no law that says that processes occur physically towards the energy minimization of the system however, there is a law (second thermodynamic) that says that processes occur physically towards the entropy maximization 1) so, why do we need ΔG (Gibbs free energy) to predetermine...

hello.. I understand what line integral of a real function mean (the area) as well explained in https://www.physicsforums.com/showthread.php?t=115057 (Mentioning this link because there line integral of a real function has been explained.) I was trying to understand what would the vector...

Ohms law is in my book stated in the form: J = \sigmaE My question is about the validity of this statement (I know it is just an empirical law, but therefore you can still think of its consequences). If the above is true then the volume current density will depend on the strength of the...