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2
votes
1answer
161 views

How to derive Eq. (1.2.17) in Polchinski?

I have a super stupid question about deriving Eq. (1.2.17) in Polchinski's string theory, vol 1. The book seems to derive from $$\tag{1.2.16} h_{ab}=\frac{1}{2} \gamma_{ab} \gamma^{cd} h_{cd} $$ ...
1
vote
1answer
331 views

Schwarzschild solution

I am calculating for many hours and I am really confused with this exercise. Consider a comoving observer sitting at constant spatial coordinates$(r∗,θ∗,φ*)$, around a Schwarzschild black hole of ...
-1
votes
2answers
2k views

Center of a mass of a hemisphere [closed]

How can I show that position vector of the center of a mass of a hemisphere is $(0,0,\frac{3a}{8})$ where $a$ is radius of a hemisphere, $x$ and $y$ axis are laying on the base and $z$-axis is ...
-1
votes
1answer
468 views

Costant volume gas thermometer [closed]

I have two constant volume gas thermometers, one with an ideal gas $pv=RT$ and the other following the Van der Waals equation $(p+\frac{a}{v^2})(v-b)=RT$. They are calibrated using the freezing point ...
0
votes
1answer
171 views

Electrons in a box [closed]

According to the Pauli principle, there can be no more than two electrons in a given state. If there are a number N of electrons in this box in the lowest states possible, show that the energy of the ...
-1
votes
1answer
383 views

Kinetic energy of a rotating rod [closed]

I have no idea where to even begin with this... Find the kinetic energy of a record of uniform density, mass 50 gm and radius 10 cm rotating at 33 and 1/3 revolutions per minute. Normally I would ...
0
votes
1answer
373 views

Is there another way to calculate the work done by air resistance?

A ball of mass $0.37\text{ kg}$ is thrown upward along the vertical with a initial speed of $14\text{ m/s}$, and reaches a maximum height of $8.4\text{ m}$. a) What is the work done by air ...
0
votes
0answers
117 views

Taking length/area element when trying to find E.resistance

I am trying to find out which 'element to take' (and why), When trying to find the resistance of some material with non-uniform resistivity $\rho$. I'll give an example: Say we have a co-axial cable ...
-3
votes
1answer
54 views

What do I need to know to calculate the price per km for plug-in hybrid or electric cars? [closed]

Knowing the per kWh price of electricity, what other factors are needed to calculate how much would one pay per km traveled on electric power compared to gasoline power? EDIT: For example, the ...
0
votes
1answer
104 views

Do photoelectrons move fast enough to use special relativity? (+ homework)

What are the speeds of the photoelectrons which are knocked out of the metal during photoeffect? Do i have to use special relativity? I am having trouble solving a homework using relativity. But if ...
3
votes
2answers
247 views

The “stationary potential energy” condition for static equilibrium in mechanical systems

I've often read that, for a mechanical system which can be described by $n$ generalized coordinates $q_1,...,q_n$, a point $\mathbf{Q}=(Q_1,...,Q_n)$ is a point of equilibrium if and only if the ...
0
votes
0answers
183 views

Coupling oscillator

I am currently doing the following problem: Two identical undamped oscillators, A and B, each of mass m and natural (angular) frequency $\omega_0$, are coupled in such a way that the coupling ...
0
votes
1answer
202 views

How to determine the region that would contain a quantum particle

(a) A hydrogen atom is in its ground state. If space is divided into identical infinitesimal cubes, in which cube is the electron most likely to be found? If instead space is divided into 31 ...
-3
votes
2answers
175 views

Vector Components and Resultant [closed]

My sister got this homework that she don't understand, me neither. Can anyone help out? Here's the problem: Give the x-component and y component of the following vectors: a. A = 7.0 cm, E b. B = ...
-2
votes
1answer
102 views

What is the alternative of PMG (Permanent Magnet Generator) in a Horizontal Axis Wind Turbine? [closed]

I need to make a report about a HAWT (Horizontal Axis Wind Turbine) and list the parts with their costs, but as a Permanent Magnet Generator is a costly thing so what can I use in alternative of this ...
-1
votes
1answer
100 views

Are the forces I'm using correct? (ball in air) [closed]

I have been working on a program which should simulate all the forces on a spherical object. Right now those are balls, but they can easily be changed to something else. These are the formulas I use ...
1
vote
1answer
142 views

Magnetic Susceptibility at Arbitrary Temperature

I'm currently working on an assignment where the questions is: Consider a gas of N noninteracting electrons in a uniform magnetic field B = B$\hat{z}$ in a macroscopic system. Assume that the ...
1
vote
1answer
512 views

Solution of 1-D Schrodinger equation for the potential $V(x) = -\frac{1}{|x|}$

May be this question might have already been asked but i couldn't find it, so let me know if its already there. Consider a potential, $V(x) = -\frac{1}{|x|}$ and if we apply this to a one dimensional ...
-3
votes
1answer
160 views

Conservation of energy

I have given one-dimensional motion of the particle directed horizontally. A problem says: "...Show that for this given motion Conservation of Energy Law holds.". Since Energy can intuitively ...
1
vote
2answers
1k views

How to find out whether a transformation is a canonical transformation?

We had a couple of examples where we were supposed to calculate the Canonical Transformation (CT), but we never actually talked about a condition that decides whether a transformation is a canonical ...
1
vote
2answers
206 views

Help with buoyant forces and liquids (high school physics)

I am stuck on this problem. Here is the scenario Suppose you send a balloon (filled with air) from your submersible craft to the surface of the ocean, $10.8 \text{ km}$ above, with the ...
1
vote
1answer
206 views

Relative angular momentum in two-particle problem

Assume the two particle problem i.e. two particles with equations of motions as follows: $\ddot{x_i} = -\frac{1}{m_i}\frac{\partial}{\partial x_i}V(|x_1 - x_2|)$ Since the angular momentum is ...
2
votes
0answers
194 views

Invariance of states under local unitary transformations [closed]

How can I show explicitly that the bell state $$|\psi^{-}>=\frac{1}{\sqrt{2}}(|0>|1>-|1>|0>)$$ is invariant under local unitary transformations $U_{1}\otimes U_{2}$ ?
3
votes
1answer
788 views

Simple thermodynamics basics - can internal energy be calculated?

Well this got me stumbled, because I've been wondering what the "question" is. One of the example examns got the following question (strangely there are no supplied solution books): A $0.2 {\rm ...
0
votes
1answer
207 views

Magnetic field, alternated current and EMF

If I apply an alternated current to a solenoid and insert into it a smaller solenoid, I could measure the induced EMF (electromotive force) and study how it changes in relation to the frequency of ...
2
votes
1answer
148 views

Mechanics of a rolling drum

I have no clue on how to approach this. The professor only discussed centripetal acceleration and angular velocity (As in $2πr\over T$ $= ωr$). Does the acceleration along the axis of the drum act ...
4
votes
4answers
1k views

Why do we take small steps while walking on ice?

When we walk on ice we should take small steps. Small steps ensure: a.)larger friction. b.)small friction. c.)larger normal force. d.)smaller normal force. The correct ...
0
votes
1answer
118 views

Finding a discontinuity and jump (time independent Schrodinger eqn)

A particle of mass $m$ is confined to move in a one-dimensional and Dirac delta-function attractive potential $$V(x)=-\frac{\hbar}{m}\alpha\delta(x)\text{ $,\alpha>0$ }.$$ Show that the function ...
4
votes
1answer
528 views

Chemical Potential of Ideal Fermi Gas

In Wikipedia's article on Fermi Gases, they have the following equation for the chemical potential: $$\mu = E_0 + E_F \left[ 1- \frac{\pi ^2}{12} \left(\frac{kT}{E_F}\right) ^2 - \frac{\pi^4}{80} ...
2
votes
1answer
679 views

Solving a time independent Schrödinger equation with a given potential

I'm trying to rework this old homework problem, and I am having problems arriving at the same solution on the answer sheet: Let $$V(x)=\begin{cases}\infty &\text{ if } x < 0\\ ...
2
votes
1answer
96 views

Cyclic integral?

Can anyone explain me what is cyclic integral and give me some instructions how to show that there exist cyclic integral for Lagrangian $$L~=~\frac{1}{2}ma^2{\dot {\theta}}^2+\frac{1}{2}ma^2{\dot ...
0
votes
0answers
367 views

Collision of 2 particles - calculating the mass and a speed after the collision

Lets say we have a particle of mass $m_1$ which has a kinetic energy $W_{k1}$. This particle collides with another same particle. How can i calculate mass $m_2$ and the speed $v_2$ of the particle ...
4
votes
1answer
174 views

The metric Tensor inside a massive shell [duplicate]

Given a fixed shell with the mass of $M$ and a radius $R$ , what would be the metric tensor for $r<R$? I do know that using Birkhoff Theorem the metric for $r>R$ should be schwarzschild. I'm ...
2
votes
4answers
141 views

Suggestions of a non-linear example for a small research project on numerical solution of ODEs?

I'm a first year undergrad and I'm doing a small research extension on numerically solving ODEs. I have done the main ODE course at my university, as well as physics. The second part of the project ...
3
votes
2answers
302 views

Unitary spacetime translation operator

Srednicki writes: We can make this a little fancier by defining the unitary spacetime translation operator $$ T(a) \equiv \exp(-iP^\mu a_\mu/ \hbar) $$ Then we have $$ T(a)^{-1} \phi(x) T(a) = ...
0
votes
0answers
37 views

Viscous force in a conductor

I was told that in a conductor there is a dissipative force and if Ohm's Law is valid for a component, the component has to be dissipative. I'm trying to prove it, but I have some problems. I know ...
0
votes
2answers
97 views

Temperature in a calorimeter [closed]

A closed calorimeter of negligible water equivalent contains 1kg ice at 0 degree Celsius. 1kg of steam at 100 degrees Celsius is pumped into it. Find the resultant temperature of the mixture. I ...
-2
votes
1answer
365 views

Normal force at the inclined plane [duplicate]

A particle mass $m$ moves down a frictionless inclined plane. Does a normal force cancels a normal component of $m$ g?
2
votes
0answers
54 views

Manipulating a formula for a relativistic Doppler shift

Lets say we take the standard configuration when $x'y'$ is moving away from system $xy$ (image 1). By knowing that the phase is constant in all frames $\phi=\phi'$ we can derive the Lorenz ...
-1
votes
1answer
106 views

Expressing a force in components [closed]

If there is an object on some ramp, how do I express its weight in terms of vectors orthogonal and parallel to the ramp surface? For example, if the object has a weight $\vec W=m\vec g$, then how do ...
2
votes
3answers
1k views

Current Through a Circuit with an 8 Resistor Setup

The following is a question from a practice Physics GRE exam (found online at ETS's website). The circuit shown in the figure consists of eight resistors, each with resistance R, and a battery ...
-1
votes
1answer
151 views

Wavefunction operators and the observable [closed]

So I got this from the exam I had yesterday. I couldn't really answer it other and it played on my mind through the night Show that if a wave function $\psi$ , is an eigenfunction of an operator [Q], ...
3
votes
0answers
162 views

Angular momentum of particle in dipole magnetic field

Basically I'm just trying to find the expression for the angular momentum of a particle of mass $m$ and charge $q$ in a dipole magnetic field. In cylindrical coordinates, ...
3
votes
1answer
133 views

nuclear physics homework

i have a homework in our nuclear physics class. the question is "An astronaut whose height in the earth is exactly 6ft is lying parallel to the axis of a spacecraft moving at a 0.9C relative to the ...
0
votes
0answers
101 views

Please correct my understanding of Clausius-Clapeyron and latent heat

As I work a problem set, I'm being asked to calculate the latent heat associated with a particular phase transition of $NH_3$ (solid -> liquid, liquid -> gas, solid -> gas). I'm being told to perform ...
5
votes
1answer
254 views

Potentials in Feynman path integral

I am trying to understand the Feynman path integral by reading the book from Leon Takhtajan. In one of the examples, there is a full explanation of the calculation of the propagator ...
4
votes
0answers
79 views

Quantum Cyclotron Frequency - Why is it off by a factor of 2?

Say you have a magnetic field $\vec{B}=(0,0,B_0)$. Then the Schrodinger Equation Hamiltonian for a spin-2 particle of charge $e$ moving in this field is: $$H = ...
5
votes
1answer
151 views

Einstein action as a functional of the tetrad (first order formulation of gravity)

Let the Einstein-Hilbert action be rewritten as a functional of the tetrad $e$ (units shall be set to $1$) such that $S_{EH}(e)=\int \frac{1}{2}\epsilon_{IJKL}~e^I\wedge e^J\wedge F^{KL}(\omega(e))$, ...
0
votes
3answers
147 views

Homework - length contraction ($\gamma$ and $u$ are unknown)

I am very sorry for posting these problems in this forum, but i don't know where to post otherwise... I have a weird special relativity problem where i get a relative speed $u$ which is larger that ...
-1
votes
1answer
199 views

Eigenvalue of Optical waveguide [closed]

Consider you have a slab waveguide having n1=3.5 and n2=1.45. The value of critical angel is 24.5 degree approx. Similarly effective refractive index will be in between 1.45 and 3.5. How can we find ...