Constant Definition and 1000 Threads

Does the presence of the cosmological constant modify the rate of expansion of the universe even during the earlier deceleratingly expanding phase of the universe?

Homework Statement I am stuck on finding ##W^u## Homework Equations [/B] I have computed the christoffel symbols via comparing the Euler-Lagrange equations to the form expected from geodesic equation. geodesic equation: ##\ddot{x^a}+\Gamma^a_{bc}\dot{x^b}\dot{x^c}=0## covariantly constant...

Hello, I'm working on my bachelor's thesis, and I ran into a problem. In the text they say: "For hot oil/watering jobs, U is typically large enough that f(t) is closer to a constant temperature than constant flux boundary condition. In the quasi-static approximation, these integrals are solved...

Background The chart above, via Lubos Motl's blog which is standard in any textbook talking about supersymmetry, illustrates the running of the the inverse of the Standard Model (SM) and Minimal Supersymmetric Model (MSSM) coupling constants with energy scale for the electromagnetic force...

A mass m is attached at the end of the string. The mass moves on a frictionless table, and the string passes through a hole in the table, under which someone is pulling on the string to make it taut at all times. Initially , the mass moves in a circle, with kinetic energy [E][/0] . The string is...

Homework Statement Homework Equations The Attempt at a Solution The normal acceleration of the particle at any instant is given by an = v2/r . v is the speed at any time and r is the radius of curvature . Minimum radius will occur when ratio v2/an is minimum . I think this will occur when...

Homework Statement A spring relaxed length is 0.5[m]. It is being pushed from both sides, and contracted to 0.4[m]. The force the spring is applying outwards is 3[N] on each side. What is the spring constant k? Homework EquationsThe Attempt at a Solution I attempted drawing a force diagram...

Hi. Is the wavefunction for x≤0 , ψ(x) = sinkx - acoskx equivalent to ψ(x) = -sinkx - acoskx where a is a constant ? Thanks

In electrical machinery and power systems, the synchronous reactance is treated as a constant reactance in series with the generated emf and is independent of load condition. These threads were very helpful for me in understanding this concept (thanks to @jim hardy!)...

Hello all. I am wondering why we raise the concentration to the exponent of the stochiometric coefficient. I understand why we take the products of reactants or products. For instance, let me give an example to show where I am getting mixed up. Let's say 2A +3B = 8C as a reversible...

Hello, I have a doubt about the Complete Set of commuting observables (CSCO) in the cases when there are a magnetic field ##B## in z. The statement is find the constant of motion and CSCO for a particle of mass m and spin 1/2, not necessary a electron or any atomic particle. I know that the...

Homework Statement the second solution is the correct, I know you can put C on both sides and it simplifed to C2 on one side, but why can't you put C2 on the right side? Homework EquationsThe Attempt at a Solution

The fine structure constant ##\alpha## is commonly cited as a very important quantity, because it gives the strengh coupling of the electromagnetic force. But it seems that the fine structure constant is not actually constant. It rather changes with the momentum of the (mediating?) particle and...

Homework Statement since specific heat c changes with temperature, but its treated as a constant in the heat formula, so that means that heat formula Q=mc(T2-T1) is just an approximation? correct? I see some texts define heat as Heat, q, is thermal energy transferred from a hotter system to a...

since specific heat c changes with temperature, but its treated as a constant in the heat formula, so that means that heat formula Q=mc(T2-T1) is just an approximation? correct? I see some texts define heat as Heat, q, is thermal energy transferred from a hotter system to a cooler system that...

do we know for a fact that the gravitational constant has always been the same since the dawn of the universe? I feel like gravitational forces should slowly be decreasing as the universe ages (meaning that assuming mass of Earth doesn't change, we should weigh a bit less in a billion years)...

In my current math class, we are constantly leap frogging throughout the text. In week 1, we did a couple things from chapter 6, not going through it fully- just a few sections here and there. In week 2, we went to chapter 3, again only doing a couple sections somewhere in the middle of the...

Homework Statement How long does it take in time constants ( = RC) for the charge on the capacitor in the circuit shown below to reach one quarter its initial value? Homework Equations C=Q/V time constant=RC Vc = Vo * (e)^(-t/RC) The Attempt at a Solution From C=Q/V I get Q=VC so for the...

Homework Statement How does an applied force and a frictional force compare when moving at constant velocity? Homework EquationsThe Attempt at a Solution

I gather rocket energy efficiency is maximal when exhaust speed closely matches the rocket speed (but oppositely directed), so to an outside observer such a rocket would leave a stationary propellant trail. I’ve found little on this model and am trying to learn more. Say we have a rocket of...

Homework Statement Homework EquationsThe Attempt at a Solution my initial approach was to just imagine the light rays leaving the focal point and emerging parrallel but then the result had no dependence on thickness how to tackle this problem how does the thickness even factor in

Homework Statement I am practicing diode circuit analysis for an ideal diode model and constant voltage drop model.I have an initial circuit shown here: Which I then redraw to look like this: I want to make sure my process in redrawing this was correct. When I attempt to get current through...

Homework Statement Two springs which have spring constant of k1 and k2 respectively are vertically hung in a series. Then, a mass m is attached to the end. Find the displacement and the spring constant of this series. Homework EquationsThe Attempt at a Solution I got the displacement x1+x2...

Homework Statement I want to prove or disprove that the dielectric constant ##K## is the projection of ##\vec E_0## onto ##\vec E## using linear algebra. Homework Equations ##\vec E = \frac{\vec E_0}{K}## The Attempt at a Solution ##(\vec E)⋅\vec E = (\vec E)⋅\frac{\vec E_0}{K}## ##K(\vec...

What is the justification for differentiating some integrals with respect to constants in order to obtain result, i.e. ∂/∂a[∫e^(− ax^2).dx] =∫-x^2.e^(-ax^2) dx?I mean what if we say "a" was 3 then differentiating wrt 3 would have no significance?How can we treat it like a multivariable function :/

Homework Statement https://i.imgur.com/f2vSXtq.png Homework Equations https://i.imgur.com/Kjy1Tzh.png The Attempt at a Solution In this question, the pressure is different at different point, in other words it is not constant throughout the system. Why the solution use c(p) (or "enthalpy" h...

Homework Statement A car is moving with a constant velocity of 18 m/s for 5 seconds, if in the next 5 seconds it travels a distance of 40 m, what is its final velocity? Homework Equations Δx= vit+ 1/2 at^2 vf= vi+at vf^2 = vi^2 + 2a (Δx) The Attempt at a Solution So I tried doing it different...

Hi! Can anyone help me? If a constant number h of fish are harvested from a fishery per unit time, then a model for the population P(t) of the fishery at time t is given by: dP/dt = P(5-P) - h, P(0) = P0. a. Solve for the IVP if h = 4. b. Determine the value of P0 such that the fish...

Homework Statement A car, length 2.4m, traveling at 26m/s wants to pass a large truck, length 12m, also traveling at 26m/s. If the car can accelerate at 4.4m/s2, how much time will it take the car to pass the truck (note the back of the car has to be in front of the truck)? How far will the car...

Hello, I just did a practice physics problem that asked if an object with constant acceleration can change direction twice. The answer was no. What if you had an object attached to a string spinning at constant velocity. Is the tangential acceleration constant?

i was reading about CSI and the first paragaph said "A constant current source is assumed here, which may be realized by using an inductance of suitable value, which must be high, in series with the current limited dc voltage source. " and it says nothing else about it , so clearly it's a basic...

Hi all, Just a clarification to ask about: if a have an electron (all by its lonesome) in its ground state, it will have non-zero kinetic energy (zero-point energy), even at absolute zero. This should mean the particle (oscillating field excitation in QFT) is always moving. Now, to be clear...

Homework Statement A constant volume gas thermometer contains a gas whose equation of state is (p+\frac{a}{V^2_m})(V_m-b)=RT and another, of identical construction, contains a different gas which obeys the ideal gas law, pV_m = RT. The thermometers are calibrated at the ice and steam points...

Homework Statement Hi, I did an experiment where I launched a soccer ball into projectile motion with my hand and took a video the situation. I uploaded it into the Tracker software to analyze it. The tracker software gave me a x-t graph, a y-t graph, and a y-x graph. From the y-t graph...

Hey, I am going to be a TA for an upper division classical mechanics class, and I'm going through the book, and making sure I can derive, or be able to justify equations used in the book. So far it has been okay, but one equation I can't justify. I will post the derivation here (or for those who...

Homework Statement Hi, I have a quick question about an experiment I am doing. I did an experiment where I rolled a ball over a flat surface and dropped a ball from a height, and I was asked if the ball rolling over the flat surface (1-d) motion is subject to constant velocity? I was also...

bromine monochloride dissociated on heating the following equation 2BrCl <=> Br2 + Cl2 .9 moles of BrCl were heated in a 5 liter vessel until equilibrium was established . the amount of free chlorine in the mixture was found to be .4 moles calculate the equilibrium constant for the reaction...

Hi, initially I would like to share this link related to derivation of maxwell equation : http://www.physicspages.com/tag/amperes-law/ My question is : in this link, it states interesting situation in electrodynamics is one where the current density is constant in time, but the charge density...

Homework Statement A hot air balloon is released from the ground & rises up with a constant acceleration of 4 m/s^2. When it is 16 meters above a sandbag is dropped. What is the time taken for the sandbag to hit the ground? Homework Equations v^2=u^2+2as v=u+atThe Attempt at a Solution...

Integral constant for internal energy of ionic liquid I have a question, and I will be really grateful if someone helps me. I have a polynomial equation for internal energy which I calculated by integration an equation of state formula, which is based on density. But, because I calculated this...

Integral constant for internal energy of ionic liquid I have a question, and I will be really grateful if someone helps me. I have a polynomial equation for internal energy which I calculated by integration an equation of state formula, which is based on density. But, because I calculated this...

Charge moving in constant linear velocity does not produce magnetic field... If not, please provide an explanation...

In the equation v=u+at, u=5 m/sec and a=0, then v=5 m/sec. That means the body is moving with a constant velocity of 5 m/sec. In a velocity-time graph, the equation produces a straight horizontal line. Some texts say the body is moving with zero acceleration and others say it is moving with...

Say I have a constant source of 1 volt that will not diminish in volts during use and would like to collect that energy how would I do it. I have been trying To figure this out for the past month and source really appreciate some help. Thanks

Homework Statement ## \psi(x) = N. (x^2 - l^2)^2 ## for ##|x| < l , 0 ## otherwise We have to find N such that this wavefunction is normalised.2. The attempt at a solution I tried expanding the ## (x^2 - l^2)^2 ## term inside the integral but this integral is extremely messy : ##...

For systems whose motion is discribed by the wave equation $$ \bigg(\frac{1}{c^2} \frac{\partial^2}{\partial t^2} - \vec{\nabla^2} \bigg)u \big(\vec{x},t \big) = 0$$ ##c## is the speed of light. It corresponds to different quantities depending on what the system under consideretion is. For...

Lets say that we have a rocket positioned at a certain angle with respect to the horizontal. The rocket is fired, with a constant propulsion force of . Assume that the rocket has a constant mass of kg (the gas used to propel the rocket is negligibly small). What is the optimal angle with...

Hi everyone. So I'm going through Landau/Lifshitz book on Mechanics and I read through a topic on inertial frames. So, because we are in an inertial frame, the Lagrangian ends up only being a function of the magnitude of the velocity only (v2) Now my question to you is, how does one prove that...

Homework Statement A vehicle Accelerates from rest (a) and travels a certain distance s1 It then deccelerates (a) at a constant rate and travels a second distance s2 until it stops. If s2/s1 = K then what is the accleration (a) of the vehicle. Homework Equations v=u+at s=ut+1/2at^2...

I read in some scripts that equilibrium constant for an ideal gas is not a function of pressure: But that is not generally true! Since: $$\left (\frac{\partial \Delta_{R} G}{\partial p} \right )_{T,\vec{n}}=\Delta_{R} V$$ and $$\Delta_{R} G^{0}=-RT\cdot \ln K$$ it should be: $$\left...