What is Change: Definition and 1000 Discussions

Hello,I would like some help for a problem Homework Statement Initially:At t=0 [/B]the cylindrical capacitor of capacitance c=\frac{\epsilon s}{d} (d the distance between the 2 electrodes and s their surface; \epsilon = \epsilon(T) is the dielectric permittivity) is discharged and we close the...

One of the Snowball Earth periods geology has been able to find went into its all (or almost) Earth frozen all over state, in a geological moment (estimated at 1,000 to 100,000 years). Science news article here.

MODERATOR'S NOTE: I have been having difficulty explaining to this member the error in his algebraic development, in particular being cavalier in his attentiveness to proper algebraic manipulation of signs. I explained his error in post #7 (and the problems that could arise if he continues to...

If I have a chemical reaction in closed system, how can I evaluate the change in T and P? I have: - one equation for the chemical equilibrium - one equation for the energy balance but I need an other one! entropy balance, maybe? Thanks Ric

Such as, Chern insulator, normal insulator, topological insulator, do they have any discontinuous change in thermal quantities? Do they have order parameters?

My question is about why the frequency of light or another EM wave does not change while passing through a medium. We know their Speed decrease and wavelenght change but think about this analogy for ex i am 4 meters high and drop 5 balls in 5 seconds and my friend waits at ground he will receive...

Homework Statement Some gas at 300K is enclosed in a container. Now the container is placed on a fast moving train.is the change in temperature of the gas the same as the change dT observed when train suddenly stops? Homework Equations 1/2mv^2=dU?? or dU=0?? The Attempt at a Solution...

Hello! (Wave) I want to solve the equation $xu_t+uu_x=0$ with $u(x,0)=x$. There is a hint to change variables $x \mapsto x^2$. I have tried the following. Let $x=y^2$. Then $u_x=\frac{du}{dy} \frac{dy}{dx}+\frac{du}{dt} \frac{dt}{dx}=u_y \frac{1}{\frac{dx}{dy}}=\frac{1}{2y} u_y$. Thus...

Homework Statement The capacitor is changed so that the largest possible current is supplied by the source. Enter the value of the capacitive reactance when this change is made. Give your answer in Ohms (Ω). A unit is not required with your answer. Homework Equations The circuit is powered by...

Homework Statement The mass of an electron is 9*10^-31kg. Find the charge in mass of a charged body if it loses 1 Coulomb of negative charge. Use your answer to explain why electricity was originally thought to be weight less. 1 coulomb = 6.642*10^18 elementary charges. Homework Equations...

Hello I plotted a graph of velocity against time only to realize that I needed more space on the X axis, so I changed my scale from instead of 2cm= 10 seconds to 2cm =20 seconds. My Y axis remained constant with a scale of 2cm= 10 m/s However, the gradient I got from the first scale was...

Homework Statement Homework Equations Current cannot change suddenly through inductor unless input is impulse voltage source. The Attempt at a Solution since input is DC source we have i(0+) = i(0-) so we have di/dt at t = 0+ is 0. Is it correct? Book has mentioned answer as B which is weird...

I am getting ready for exams and I have encountered this problem on the exam paper: In AC circuit there is a condensator and a inductive coil, At first XL=XC, how does the relation change when the frequency doubles? The answer says XL=4XC Can someone explain me how they come to this conclusion...

Homework Statement A pipe has a square cross section and a width of 2.00 m and is used to transport salt water from the ocean into a desalination plant. If a pump pushing the water into the pipe at a depth of 1.00 m below the surface of the ocean does so with a pressure of 80 kP a, and the...

Have experiments been done to measure the red shifts of distant objects over time? If inflation is correct, the the speed at which an object is receding relative to us is based on how far away that object is located. Therefore, the most distant objects would also have the highest acceleration...

The energy of a photon depends on its wavelength, so theoretically when it is blueshifted it should have more energy right? Then what if a spaceship with a solar panel on the front is traveling towards the sun at relativistic speeds. An incoming photon undergoes a blueshift from the observer on...

\begin{align}\displaystyle &=\int_{0}^{8}\displaystyle \int_{\sqrt[3]{x}}^{2} \frac{dydx}{y^4+1}&&(1)\\ &\qquad D: 0\le x \le 8, \quad \sqrt[3]{x}\le y\le 2 &&(2)\\ &=\int_{0}^{2}\int_{0}^{y^3} \frac{1}{y^4+1} \, dxdy&&(3)\\ &=\int_{0}^{2}\frac{y^3}{y^4+1} \...

We know that reflected light undergo a phase shift of π in EXTERNAL REFLECTION but there is no phase shift in INTERNAL REFLECTION . Does this violate Stokes Relation, which states that every reflected beam undergo of phase shift of π ?

Homework Statement Match the following Given : Processes do not include chemical reactions. Assume CP,m and CV,m are independent of temperature for given substance and consider only pressure-volume work in given all processes. Homework Equations ΔU = Q - W ΔH = ΔU +...

Hello, I am a student in Coventry, UK working on Phase Change Problems and going through 1-Phase Neumann Analytical solutions. As per most books, or specifically Mathematical Modeling of Melting and Freezing Processes chapter 2 (attached) page 36, equation 15, the general equation of...

I'm looking to see how much the dielectric constant of air will change mostly as a function or air temperature. Is there a formula that outputs air dielectric as a function of temperature or atmospheric pressure?

It seems that a solution to the following problem is strangely absent from the internet. After days of research, I have found no one who offers such a solution. Only one paper addressed it but was sloppy in the way it presented the equations; they were incomplete. The problem is simply...

Homework Statement Calculate the change in molar entropy of steam heated from 100 to 120 °C at constant volume in units J/K/mol (assume ideal gas behaviour). Homework Equations dS = n Cv ln(T1/T0) T: absolute temperature The Attempt at a Solution 100 C = 373.15 K 120 C = 393.15 K dS = nCvln...

Homework Statement Let 3/2kT be the kinetic energy of ideal gas per molecules. T the absolute temperature and N the avogadro number. Answer the following questions : 1) when the volume doubled at constant temperature. How many times the kinetic energy per molecule become greater than before...

Homework Statement Homework EquationsThe Attempt at a Solution 19800*.35 = 6930J

Homework Statement Adiabatic expansion of an ideal gas is carried out in a steady flow process. The initial pressure of the gas is 2.5 bar. The volume is expanded from 1.2m3 to 3.8m3. Heat capacity ratio (γ) = 1.42. Calculate enthalpy change of the process. Homework Equations PV = nRT W = ∫...

Homework Statement A 77.1 kg hiker uses 191 kcal hr-1 (converted to 222.133 J.s ?) of energy whilst hiking. Assuming that 20% of this energy goes into useful work and the other 80% is converted to heat within the body, calculate the temperature change, in units of Kelvin (K), of the hiker's...

Information Given:In 1956, Frank Lloyd Wright proposed the construction of a mile-high building in Chicago. Suppose the building had been constructed. Question: Ignoring Earth's rotation, find the change in your weight if you were to ride an elevator from the street level, where you weigh 708...

Been reading basic stuff about the astrophysics behind the prevalence of various elements, curious at what rate this changes over time. The Milky Way is something like 14 billion years old. At first it was all H and He then heavier elements were created and distributed through supernovae...

Hello. Galileo claimed that a body could not "by itself" change the state of rest or uniform rectilinear motion of its center of gravity. Newton clarified this with the notion of force and inertia. F = m.a. So let's follow a mass m. Either a closed container containing a gas. And one of the...

I am not sure how I should set my u and v expressions into the u-v plane for this question. How should I look at the expression to set u and v expressions?

I have obtained as such using changing of variables/ transformations: Let u= y/x and v= xy after manipulating the equation of the curves as such xy = 5, xy = 2, y/x = 1 and y/x = 4. Then u = 1, u = 4, v = 5 and v = 2 => obtain a square on the u-v plane. Change the integrand to: Outer...

Say I dissolve NaOH in water - a very exothermic reaction. Does it matter if I dissolve it in water that is at room temperature or at a different temperature? Will changing the initial temperature of the water affect the dH of the reaction (hence affect the change in temperature at the end of...

The question is to find the change in kinetic energy of a system. the system in use is a pully system with a wooden block on a flat surface attached to a 100g mass. I have calculated force of friction between the block and desk, and using a ticker timer, I have individual speeds at every 0.1 of...

Does the speed of light change in different substances, or does it seem to change because it gets absorbed and emitted by all the particles?

I just went on a Japan trip. In the airplane, besides throwing up my ball and phone, I was doing a little bit of studying. While the plane was in takeoff, in the middle of flying, and landing, I noticed how the wing positions changed. I already know how takeoff works. It works when the plane...

Hello! The equation for relativistic mass by special relativity tells us the relativistic mass for object in motion...but since inertia mass has same value as gravitational, does this formula also apply for gravitational mass? Thank you!

Hello, I would like to know, why is the volume of gas produced during phase change significantly more than the original volume of the liquid being used? Say water changing phase at 1atm.

Can dx be thought of as a sufficiently small change in x? I want to say that dx is the change in x and change in x approaches 0, but that would just be 0. So I think it might make more sense to just say sufficiently small. Then when we look at something like a derivative dy/dx we can look at...

Firefox 59 intermittently displays only part of content on a page if i click menu bar and change magnification up or down one setting, ie from 100% to 90 or 110 it finishes but if change back to initial magnification it disappears again windows 7 firefox 59.0.1 anybody else seen that ? old jim

I was reading about astronaut Scott Kelly's genes having "permanently" changed after a year in 0-G (the key is not that his capsule was in space, but rather that he was at 0-G, but I digress ...) Is it supposed to mean that genes have changed in new cells being born, eventually taking over as...

Suppose a ocean wave encountered a section of ocean which had a higher level of aeration from gas such as methane escaping from the seafloor. Due to the aerated sections apparent lower density would the wave travel slower through the aerated section than its propagation speed thru pure seawater ?

Greetings, I have very little experience with fluid dynamics and I was wondering how I can calculate a pressure drop across an abrupt change in diameter of the piping used for water. Any help is appreciated! Thanks!

If electrons are waves, what causes them to change direction and move up and down?

I currently have education in religion, and at 46 years old, I have the desire to go back to school and study astronomy/physics etc.. i would be starting all over and would take til I am 55 if i go post doctorate. My interest in astronomy started when i was 12. if i had attended a better school...

Homework Statement As an electron (q2) moves from point A to point B, it moves farther from a positive charge (q1). Does the electric potential energy increase, decrease, or stay the same. Homework Equations U=-kq1q2/r The Attempt at a Solution The electric potential energy decreases in...

Homework Statement If water vapor is assumed to be a perfect gas, molar enthalpy change for vaporization of 1 mol of water at 1 bar and 100 C is 41 kJ/mol . Calculate the internal energy, when 1 mol of water is vaporized at 1 bar pressure and 100 C. Homework Equations $$\Delta U = \Delta H =...

If you could change the way we educate people, what would you do? I leave this as a general open-ended question.

Hi, I have a little conceptual question. I have an idea about the topic, but I would need to formalize it a little bit. The problem is the following: Imagine the following scenario: You put a little bit of water in a bottle, you assure yourself that everything as at a constant temperature and...

Is the pattern of temperature variation of the cosmic microwave background static, or does it vary over time?