# Search results

1. ### Lagrangian for a Spherical Pendulum (Goldstein 1.19)

Homework Statement Find the Lagrangian and equations of motion for a spherical pendulum Homework Equations L=T-U and Lagrange's Equation The Attempt at a Solution [/B] I found the Lagrangian to be L = 0.5*m*l2(ω2+Ω2sin2(θ)) - mgl*cos(θ) where l is the length of the rod, ω is (theta dot)...
2. ### Computational Introduction to Computational Physics Texts?

Hi all, I'm starting graduate school and really need a better handle on computational physics. I'm not extremely experienced with MATLAB and haven't used Python or anything else. Does anyone know a good textbook to get me started? I looked in the textbooks links to this forum thread and the...
3. ### A Raman Spectroscopy vs. Inelastic Electron Tunneling

I am a first year graduate student in physics and am becoming familiarized with Raman spectroscopy to study structure of materials based off of their vibrational states. In some personal study outside of this, I came across the idea of inelastic electron tunneling spectroscopy (IETS) and was...
4. ### Lagrangian Mechanics Problem

Homework Statement We have a particle of mass m moving in a plane described by the following Lagrangian: \frac{1}{2}m((\dot{x}^2)+(\dot{y}^2)+2(\alpha)(\dot{x})(\dot{y}))-\frac{1}{2}k(x^2+y^2+(\beta)xy) for k>0 is a spring constant and \alpha and \beta are time-independent. Find the normal...
5. ### Ability to measure distances with parallax versus size

I would like to preface this by stating that I am not very well-versed in cosmology or astrophysics, but I've been thinking: I understand the idea of parallax, both in the sense of human eyes measuring distances to nearby objects and in the sense of telescopes on earth (or in orbit) measuring...
6. ### Nonlinear Regression Curve Fitting

This isn't a precise homework question, but this seemed like the most reasonable place to post. If not, please feel free to move it. I have a large set of data points that should fit to a known equation (the Drude-Smith model for conductivity) The equation the data should fit to is: σ(ω) =...
7. ### Photovoltage Question

Before I get into my question, it is helpful to note the paper I am referring to. "Photovoltage in nanocrystalline porous TiO2" by V. Duzhko, et al. DOI: 10.1103/PhysRevB.64.075204 In Section B. "Spectral photovoltage in well-passivated porous TiO2 layers", the authors mention that "The...
8. ### Modeling Quadratic Air Resistance in 2-D using Mathematica

Homework Statement I am working on a little project in which I analyze a video I found online and try to determine if it is real of a hoax. The video I am analyzing includes a man throwing a football off of a football stadium (at the very top) and making it into a basketball hoop at field...
9. ### Phase space diagram for a spring in simple harmonic motion

Homework Statement A mass m = 750 g is connected to a spring with spring constant k = 1.5 N/m. At t = 0 the mass is set into simple harmonic motion (no damping) with the initial conditions represented by the point P in the phase space diagram at the right. **(This phase space diagram has...
10. ### Simple proof regarding integers

Homework Statement Show that if m and n are integers such that 4|m2+n2, then 4|mn Homework Equations The Attempt at a Solution Since 4 divides m2+n2, then we can say that m2+n2 = 4k, where k is an integer. I haven't done any mathematical proofs of any kind yet, but we were supposed to see...
11. ### Basic Linear Algebra Problem

Homework Statement The vectors that are perpendicular to (1,1,1) and (1,2,3) lie on a ____. Homework Equations The Attempt at a Solution This is really straight forward, but I cannot validate the answer to myself. The textbook says that they should lie on a line, but why is this? Obviously...
12. ### Studying Quantum Mechanics Textbooks Problem

Hi everybody, I am currently a Junior in college studying Physics. I am planning on going to Graduate School, which obviously requires the GREs. I have looked up that the physics GRE is 12% Quantum Mechanics (as per this source here). However, how my University is set up, I will not be able to...
13. ### Using Method of Imaging for two point charges between Parallel Plate Capacitors

Homework Statement Use either image charge method of separation of variables to solve: The distance between two large, grounded parallel conducting plates is 4x. Between them, two point charges +Q and -Q are inserted and have a distance x and 3x from one of the plates. (A line connecting the...
14. ### Using the method of Mirrored Charges to find the charge force due to grounded sphere on 2 charges

Homework Statement Two point charges of equal value are placed a distance 2b from one another. In the middle, there is a grounded conducting sphere. What is the minimum radius of the sphere required to cancel out the repelling force between the two charges? (Solve using Image Charge Method)...
15. ### Proving various properties of complex numbers

Homework Statement This problem is very easy, but I'm not sure how best to "prove" it. This part of the question just states: Prove that (1/z)* = 1/(z*) where z* is the complex conjugate of z. Homework Equations The Attempt at a Solution So the complex conjugate of z = x + iy is defined...
16. ### New to MatLab: Having some trouble

Homework Statement This isn't really for homework, but I wasn't sure where else to put it. anyone wishes to move it, that is fine. I'm just getting into some research and I was tasked with reading data from a text file into MatLab and then graphing it by fitting it with exponentials. I am very...
17. ### Euler's Method to approximate a second order Differential Equation

Homework Statement y'' + 4y' + 4y = 0 ---- y(0) = 1, y'(0) = 5 Find the exact solution of the differential equation. Use the exact solution and Euler's Method to compute Euler's Approximation for time t = 0 to t = 5 using a step h=0.05. Plot Euler's & Exact vs. t and plot Error vs. t. Then...
18. ### Solving for Velocity as a function of height (y) with quadratic drag

Homework Statement Write down the equation of motion for the downward journey of a baseball subject to quadratic drag. Find v as a function of y and, given that the downward journey starts at ymax (given below), show that the speed when the ball returns to the ground is: vterv0 /...
19. ### Projectile Subject to Quadratic Air Resistance

Homework Statement A projectile that is subject to quadratic air resistance is thrown vertically up with initial speed v0. (a): Write down the equation of motion for the upward motion and solve it to give v as a function of t. (b): Show that the time to reach th top of the trajectory...
20. ### Stimulated Emission Question

I have been learning some introductory quantum mechanics and stimulated Emission is giving me some problems conceptually. I understand that photons can be absorbed to bump electrons up to higher energy levels and that electrons in the higher energy state spontaneously decay back to the lower...
21. ### Kinetic Energy Question

In my theoretical mechanics class, we went over some very basic conservation laws (namely momentum) and talked about colliding masses. Say you have 2 masses, m1 and m2. m1 is moving to the right (towards m2) with velocity v. m2 is stationary. After the two masses collide, m1 recoils with...
22. ### Row Reduction to solve for 6 Unknowns

Homework Statement I am in a calculus class where we are learning the introduction to row reduction. I have done this before in other courses, so I am familiar with the process, but I am not sure about this one. We were given: x4 + 2x5- x6 = 2 x1 + 2x2 + x5 -x6 = 0 x1 + 2x2 + 2x3 - x5 +...
23. ### Introduction level Solid State - Mean free time/path & lattice spacing

Homework Statement Silver has a density of 10.5E3 kg/m3 and a resistivity of 1.6E-8 Ω*m at room temperature. On the basis of the classical free electron gas model, and assuming that each silver atom contributes one electron to the electron gas, calculate the average time, Tau, between...
24. ### Fourier Integrals and Division

Homework Statement (a) Find the Fourier transform f(ω) of: f(x) = cos(x) between -pi/2 and pi/2 (b) Find the Fourier transform g(ω) of: g(x) = sin(x) between = -pi/2 and pi/2 (c) Without doing any integration, determine f(ω)/g(ω) and explain why it is so Homework Equations f(ω) =...
25. ### Fourier Series/Transformations and Convolution

Homework Statement (f*g)(x) = integral from -pi to pi of (f(y)g(x-y))dy f(x) = ∑cneinx g(x) = ∑dneinx en is defined as the Fourier Coefficients for (f*g) {the convolution} an is denoted by: en = 1/(2pi) integral from -pi to pi of (f*g)e-inx dx Evaluate en in terms of cn and dn...
26. ### Volume of a solid with 3 boundary conditions

Homework Statement Find the volume of an object bounded by x2 + y2 ≤ 1, x2 + z2 ≤ 1 and y2 + z2 ≤ 1. Homework Equations The Attempt at a Solution This stuff is very new to me (multiple integrals to find volume) so I am not entirely familiar with it. My first thought was to put...
27. ### 1-D Quantum Mechanics Conceptual Problem

Homework Statement The probability density at certain points for a particle in a box is zero. Does this imply that the particle cannot move across these points? Explain. (I found a picture online here). Homework Equations The Attempt at a Solution In a particle in a box, you can...
28. ### Minimizing a multivariable function

Homework Statement Find the shortest distance from the origin to the surface x=yz+10 Homework Equations The Attempt at a Solution So I said that my main function, f(x,y,z) = x^2 + y^2 + z^2 (the function I want to minimize) Then I said that g(x,y,z) is my constraint function...
29. ### Bohr's Correspondence Principle and quantum theory

Homework Statement Does Bohr's correspondence principle apply only to quantum theory? Can you give an example of the applications of this principle to relativity theory? Homework Equations The Attempt at a Solution According to my textbook, Bohr's Correspondence Principle simply...
30. ### Matter/Electron Waves and the Davisson-Germer Experiment

Homework Statement This is a conceptual question that I am not quite sure about. In the Davisson-Germer Experiment (details here), do the electron diffraction peaks that occur only show up if the incident beam of electrons hits the crystal surface perpendicularly? Homework Equations...