Difficulties Definition and 77 Threads

Adrian Cho, who is always excellent, has a very good article on the recent difficulties Fermilab has been having: https://www.science.org/content/article/trouble-and-strife-deepen-famed-u-s-particle-physics-lab A little background. In 2007, the current contractor received the DOE contract to...

I'm having difficulties finding the current for a 9-ohm resistor only, not the 20-ohm My attempt was to find the voltage of a 20ohm resistor which is V = (0.75A)(20-ohm) = 15V. I got the 0.75A by adding the currents of the two resistors (8-ohm and 16-ohm) together that were in parallel and it...

The risbon model model was inveted by Harari in 1981. It is a theory that lies beyond the standard model and explains the existence of quarks and leptons on the basis of jusr 2 elementary particles, the T- and V-rishon (heuristically that is, like the quark model did once for the plethora of...

I have been developing a SPAD based photometer having a 10 ns deadtime, near-zero dark counts, near-zero afterpulsing, and that is temperature independent (within a reasonable range). It works well with photon level pulsed optical signals, (10ns to several microsecond pulse widths at rates up...

Hi guys, I'm having trouble computing a pass 1 to 106.15. It's in the pictures. So, what a have to do is the derivative of ##f## with respect to time and coordinates. Then I need to rearrange the terms to find the equation 106.15. I am using the following conditions. ##r## vector varies in...

Now I realize this is not the simplest way to do this problem, I get that, so please don't answer me with the "Try doing it this way..." posts. I would like to see if we can please make this solution come to life. The first kink in the proof is the functional equations, I know it should work...

I'm new to using Octave 5.1.0, and a bit confused about how to solve ODEs with Octave. Let me show you a bit of code that I grabbed off a university web site: >> function xdot = pend(x,t) % pend.m xdot(1) = x(2); xdot(2) = - x(1) - 0.1*x(2); end >> sol=lsode( "pend",[0.1, 0.2], t =...

Hi all, I just wanted to know if anybody else here has experienced this sort of mass rejection from anything and everything. I've finished my Bachelors (3 year) and Masters (both in physics) from a not-so-great college in India. I've been applying to every single opportunity that comes my way...

Can any expert tell me have we overcome some/most of the difficulties described in chapter 3 of Ashcroft and Mermin in the Free Electron Model since the textbook was written? In the cases that we have, what exactly did solve the difficulties described in this chapter? If you want me I can copy...

Hello. I plan on being a doctor when I finish high school, but I’ve had some trouble with science. My grades aren’t bad or anything but right now, I find biology dull and boring. We’re learning about cells, mitosis, and similar stuff and I just can’t get into it. Does this mean life sciences...

I can obviously do the chain rule and see how the final expression of the derivative is related to the original function but I can't seem to figure out the substitution Rule as an intuitive way of solving the indefinite integral of functions... bear with me if I'm too verbose, I've attached an...

Hello. I wonder if I can take some of these resistors off and make the signal stronger without breaking the rest of the components. Is this possible? Also why are the non-trimming capacitors needed? I have a picture attached. Thank you!

I need to know how to attach a wheel to an axel, but first of all, i need an axel with a gear pre-built into it. The axel needs to be over 20 inches long (because that is the width of my vehicle) and support bicycle/tricycle wheels. Does anyone know of such wheels and axels? (The wheels have...

Hello. I am working on planning to build a small pnumatic tricycle. I got far in my calculations, but not quite finished because I am stuck. If someone could check my math, that'd be great, but my problem starts at the second line. ______________________________________________ 1. Let's say...

Hi all, I am an undergraduate Physics student. I have recently realized that I am extremely bad at solving "new" problems related to the topics I am working on. Trying to do any question that deviates slightly from the norm will cause me to be stuck on that problem for hours, usually to no...

Hi Me and a couple of class mates are working on our bachelor's project of which the mission is to measure the temperature of the sun using a parabolic antenna. We are having great troubles trying to come up with an equation relating the antenna temperature (which we are able to calculate with...

Homework Statement R(ABCDEF) D->F AB->C E->F C->BD D->E Decompose R into dependency preserving 3NF Homework Equations F = {D->F, AB->C, E->F, C->BD, D->E} The Attempt at a Solution My attempt is to first construct the minimal basis for the FD set F, which is G={A->C, E->F, C->B, C->D, D->E}...

I'm reading an introduction to relativity which uses different notation to the standard indices used in my college course. I came across: L(\nu)gL(\nu)g = 1 Where L is the Lorentz transformations four-vector and g is the metric. Without the indices, I'm a little lost. Is there some convention...

It's rather strange, isn't it? I did just fine in Algebra I, and even better in Algebra II, but now that I'm in Calculus I I'm finding that my algebra skills aren't as sharp as I thought they were. Often times i'll get the calculus portions of problems correct, but when it comes down to...

haruspex submitted a new PF Insights post Conceptual Difficulties in the Roles of Variables Continue reading the Original PF Insights Post.

Hello, Thanks to all of you for the help that you provide so that we can move forward. I need help about the computation of the Kretschmann scalar without using software, I face to some difficulties on its computation for instance in the case of Schwarzschild metric. Could some one help me with...

Homework Statement Here's a graph of displacement it wants me to make: http://s15.postimg.org/7v1x5najv/graph.png. I tried that graph in the picture as the answer but it didn't accept it. There are no numbers or specifics for Figure 1 they give you, so I'm confused on what to do. Very strange...

Hi guys, this is mainly a question to people who have completed a degree in physics already, but I would love replies from anybody who has a opinion, or has had a similar experience. I am in the third year of a masters degree in physics. As I have progressed through the degree things have...

Homework Statement Hi, this is my first time posting so if there is any advice on how to make this post cleaner, please tell me! I've been stuck on a problem and I can't figure out what I'm doing wrong. I have attached the problem and the attempt at solving the problem below. I am supposed to...

I will study gravitation quantization(string theory or canonical quantum gravity),so I want to know what are the difficulties of gravitational quantization scheme.I know that quantization means that calculating commutator of quantum field operators via Poisson brackets.Are the difficulties being...

Homework Statement An inductor with L = 50 mH is in series with a resistor of R = 180 ohms. At t = 0, a potential difference of 45 V is suddenly applied across the series circuit. At what rate is the current increasing after 1.2 milliseconds? Homework Equations V = IR + Emf Emf =...

Hi everybody, I am having some difficulties graphing this decaying trig function: ((e^(((.175(1-(y/10))+((y/10)-.001))t)/(2000)))(10cos((sqrt(((.175(1-(y/10))+((y/10)-.001))^(2))-400000000))t)+10sin((sqrt(((.175(1-(y/10))+((y/10)-.001))^(2))-400000000))t)) I have checked over the...

Homework Statement I am struggling with implicit derivatives, and though my course book includes final solutions to odd numbered exercises, it does not show the work. As such, I'm stuck in the process of getting from point A to point B: Find the derivative y'(x) implicitly of...

Greetings PFers You’ve probably heard of the new “revolution” called Li-Fi (Light Fidelity) which is a method of data transmission utilizing the modulation of very high frequencies in LED light bulbs. A good demonstration (And probably the first) is here...

Hello people, I'm new here, but i already read some topics with this similar question. I'm just about to finish my master degree in theoretical physics (more specifically in qft) and besides i have really enjoyable moments studying it... I feel that something isn't right. It's a hard area...

Hello, I am having troubles ridding my research paper of this thorn in my side: It is a rather random line of dots. I have tried everything in my power to remove it, but to no avail. I am, for some odd reason, unable to highlight it. Furthermore, temporarily deleting the surrounding...

I hope you can bear with me as I warm up to my question regarding Brownian motion. I am currently studying physics on my own and am watching a series of lectures on Quantum Theory. Obviously I am just some guy with an interest in physics and I have no clue. Apparently, Brownian motion is the...

I'm a 3rd year major in physics. Unfortunately, I come from a pretty poor family and I study away from home, and we've been hit by an economic disaster that forces me to abandon college. I'm pretty good in my studies, I got a scholarship and I was at the top 10 of the best students of my...

I'm creating this thread for any major difficulties I come across in How to Prove It: A Structured Approach, 2nd edition by Daniel J. Velleman. This is a self-study (with any assistance if I can get it). Homework Statement The problem is to analyze the logical form of the given statement...

Hello all, I had a question about Electromagnetic waves. Although it isn’t homework (just to settle something in my own mind) I thought this would be the best place to put it. Perhaps it would be best if I could explain a situation I could understand and then hopefully someone could bridge...

How likely is it that an educated (technical and writing background) but not professionally experienced technical writer could make it in the industry if she has difficulty processing verbal information and general (noticeable but not severe) social discomfort? What specific kind of work...

First of all, I've already had and scheduled SEVERAL appointments with a psychiatrist, and I'm not asking for self-diagnosing advice - I'm simply wondering what I should look forward to after all the checking is done.So let me begin with a list of symptoms that I'm experiencing, or have...

Hi, this is my first post. I'm generally more of a blog/message board reader than a contributor, but there's really been something that has been eating away at me, making it difficult for me sleep at night. (Note: long post coming up) Last semester in Organic Chemistry I, I made a huge...

I am trying to prove to myself that the most probable distance for a 1s electron in a H atom is the Bohr radius. The probability of finding an electron (for any given state in a hydrogenic atom) in a spherical shell of thickness dr at a distance r from the nucleus is \left|R_{nl}\right|^{2}...

This is another problem than I've been stuck on for a long time and I tried reading and watching videos but I only find first order partial differentiation with more than two variables or higher order partial differentiation with only two variables. (I'm not calling f a variable but I am calling...

So at the moment I'm getting ready to begin directed studies with a professor who is a bit impressive compared to the rest of the schools faculty (at least on paper! I do not know if he is a great teacher yet) with his B.S. in Physics (w/Honors) from Caltech and his Master from Oxford and even...

Hi All, This is really a stupid question...I can't seem to get my head around it and it's making me depressed just thinking about it. Anyways, let's consider \mathbb{R}^{n} the set S = [0,1] is not compact (I know it is but I can't see the flaw in my argument which seems it should be...

Dear Friends, I encountered with some difficulties in solving following PDE (off course, analytically not numerically), so I would really appreciate it if you help me in this matter. The PDE is: Uzz+f(t)*Uz=g(t)*Ut where U(z,t), f(t), and g(t) B.Cs and I.C are: U(0,t)=b...

Just working through a problem Acheson's book (From Calculus to Chaos) if anyone knows it.. eq 8.6 in this book.. As he's working through the problem he makes the step of this: m\int_{t_{1} }^{t_{2}} \left( \dot{y}_{\scriptscriptstyle A }\dot{\eta} - g\eta \right)\,dt (1) to...

A momentum question - having conceptual difficulties - please help..! Homework Statement A freight car of mass M contains a mass of sand m'. At t = 0 a constant horizontal force F is applied in the direction of rolling and at the same time a port in the bottom is opened to let the sand...

Homework Statement "The threshold frequency of a particular metal surface is 5.6 × 1014 Hz. Calculate the maximum kinetic energy of emitted electrons if the frequency of the light striking the metal surface is double the threshold frequency." Taken from AQA Physics Exam 2009 Homework...

Homework Statement Question attached Homework Equations The Attempt at a Solution I'm mostly wondering with c) and also want to check if my solution is correct. My solutions for this question are: u(x,t)= -1/2 for x <= -1/2*t = 1 for -t < x < 1-t = 1/2 for x =>...

Hello, everyone. Excuse me but I think I should post this question in sub-forum Calculus & Beyond Learning Materials but I can't access to that sub-forum and so... The question is: I began to learn to work with Maxima and I have several doubts. The help of the program is a little...

I face some difficulties to find the domain Now i put my questions and please help me to answer it i try solve it thanks

Hello. I want to know the branches of Physics in order of their difficulty. I am in 10th grade and am going to be 15 in 3 days. Happy b-day to me :). Thanks for any help.