What is Change: Definition and 1000 Discussions

In a degenerate n type semiconductor, when the doping concentration has a gradient(say -ve gradient), then how fermi energy level and intrinsic Fermi energy levels will depend upon the concentration gradient? ~If anyone knows anything about it, kindly help.

Mod note: Based on an attachment in a later post in this thread, the actual expression is ##(9 - 16\cos^2(\theta))^{3/2}## Homework Statement : https://www.physicsforums.com/posts/5610105/ Homework EquationsThe Attempt at a Solution my working is (9^1.5) - (16^1.5)[ (cos theta)^1.5 ] =...

I am trying to derive from the Lorentz force equation the time derivative of the total energy. This involves using the equation for the jth electron in an electron beam traveling through an undulator. I have done it in such a way using the work done relation however I have been told that it is...

Homework Statement We just started capacitors in class and we were introduced to the formulae q=CV and i = C*dV/dt In the notes it said that if the voltage across a capacitor were to change instantenously, the capacitor current would be infinite. It goes on to say why this is never possible...

In the principle study of the Pioneer Anomaly, John Anderson and Slava Turyshev suggested a speculative explanation for the apparent deceleration of the spacecraft : as an acceleration of the clock rate used for telemetry back on earth. To be clear, this explanation has been discounted-...

Homework Statement A disk of mass m1 is rotating freely with constant angular speed ω. Another disk of mass m2 that has the same radius is gently placed on the first disk. If the surfaces in contact are rough so that there is no slipping between the disks, what is the fractional decrease in the...

Homework Statement The coefficient of static and kinetic friction is constant for a specific surface. On an incline plane s and k are both equal to tan of the inclined angle. If the angle increases then tan changes which means the coefficient of friction changes. How is this so? Homework...

What properties have to do with the frequency at which the lengths change of the arm? Also does anybody have a body paper or webpage which explains the properties at a detailed level?

Homework Statement (a) What is meant by the statement that a solenoid has an inductance of 2.0 H? A 2.0 H solenoid is connected in series with a resistor, so that the total resistance is 0.50 Ω, to a 2.0 V DC supply. Sketh the graph of current against time when the crrent is switched on. What...

Homework Statement You have to graph f(x) = x3 - 2x2 + x and find where the instantaneous rate of change is positive negative and zero. Homework EquationsThe Attempt at a Solution I factored this and found the zero's to be x= 0 and x = 1. With all this info given I graphed it and realized...

Homework Statement A closed wire loop in the form of a square of side 4.0 cm is mounted with its plane horizontal. The loop has a resistance of 2.0 * 10-3 Ω, and negligible self inductance. The loop is situated in a magnetic field of strength 0.70 T directed vertically downwards. When the field...

i and me teacher was in debate vs each other my teacher say we shouldn't believe in big bag because it is just a theory and it may change i say to him the theory is a collection of fact and model that have been on test then he say to me i have a B.S in physics do you know more than me .

Homework Statement Given: an npn transistor having VBE = 0.76V for a collector current of 10mA at T=350 K (n=1) Find the corresponding collector current for VBE = 0.70V 2. Relevant questions a) Wouldn't that temperature be way to high for the transistor to act normally?? I mean 350K is 170F...

Homework Statement This is a question for 10 year old but I have a problem understanding why the answer is so. (The student asked me this.) There are two similar containers, X and Y, with 500 ml of boiling water. X is an aluminium container. Y is a plastic container. They are then covered with...

Homework Statement [/B] I was given a graph in the PV plane of a cyclic process and asked to find some quantities, one of them is the change in entropy for the system. I just had a question about the units. Homework Equations dS = CVln(Tf/Ti) The Attempt at a Solution The data was given in...

Homework Statement A 50-kg ice skater moves across the ice at a constant speed of 2.0 m/s. She is caught by her79-kg partner, and then the pair continues to glide together. He is at rest when he catches her, and immediately afterward they both coast. Part A) What is their velocity just after...

Here is a problem that showed up on my exam that I couldn't find any variation online. A stick of length L is depth D in the water. The stick is parallel to the surface of the water, and the viewer (in air) is looking down in the water right over the middle of the stick. What is the apparent...

Homework Statement A composite system consists of an insulated partitioned volume, shown in Figure 4.9. Side 1 contains 2 mol of a monatomic ideal gas and Side 2 contains 4 moles of the same monatomic ideal gas. Initially, the two sides are separated by a fully insulated partition (adiabatic...

Homework Statement Homework Equations ΔKE=W+FcosΘd KE=.5mv^2 Final Vel^2=initial Velocity^2+2ax The Attempt at a Solution So calculate the force at x=2.6 to -5.356N, set 2.6(-5.356)=1.3Vf^2-1.3(0^2) which seemed to prove a problem as the square of the final velocity was negative, but just...

Since 97% of everyday weight scales (both in doctor offices and at home) measure our actual mass either in lbm and/or kg, and NOT force (lbf or N), then why does oxford choose to define weight to be relative? "a body's relative mass or the quantity of matter contained by it, giving rise to a...

Homework Statement Refer to the photo, please verify my answer Homework Equations calculus The Attempt at a Solution For c, can I do it by assuming Ah=V. A(dh/dt) + h(dA/dt) = dV/dt then find dA/dt?

The stars formation decreases the entropy but the radiations given out increases the overall entropy i am said ...but once the fusion processes are over the star no longer gives out radiations...and still the volume in which the matter particles of the star can be becomes less as the star...

I am learning physics on khan academy and they do a proof to show that delta G for a reversible reaction is negative and how for a irreversible reaction it is positive. However in the proof, they assume that the heat put in by the isotherm is less for an irreversible reaction compared with a...

Homework Statement A 1x106 kg piece of ice is placed into a lake. How much heat is taken from the lake to raise the temperature of the ice from 0 °C to 1x10-20 °C? How much volume does the lake increase by? Latent heat for water is 334x103 J/kg Homework Equations Found in my textbook, cice =...

Hello, We have a system with a 70 bar pump and 9 nozzles connected to the pump lines. Total flow rate is 2 l/m. Is there a way to change only one nozzle flow rate manually, with a pressure regulator valf just behind that nozzle? Thank you.

Homework Statement An ideal gas with adiabatic index γ is taken around a complete thermodynamic cycle consisting of three steps. Starting at point A, the pressure is increased at constant volume V1 from P1 to P2 at point B. From point B to point C, the gas is allowed to expand adiabatically...

Homework Statement A 3kg projectilce traveling at 100 m/s is stopped by being shot into an insulated tank containg 100kg of water. If the KE of the projectile is completely convereted into thermal energy, how much will the temp of the water increase in degrees celcius? The standard heat of...

Homework Statement Consider a thermally insulated resistor with resistance R=20 Ω and mass m=5.0 g. The resistor is made of a material with specific heat capacity c=850 J/(g-K) and carries a current of 2.0 A for a time period of 1.0 s. a) Calculate the increase in the temperature of the...

When a wheel spins does it generate lift or something, the wheel spins so that the torque force is downwards. for example you measure the weight of the wheel and then you spin then wheel does anything change? The wheel is solid and if their change something does it matter if it is a constant...

I'm studying relation between conservative force and potential energy,and getting a big question on change in potential energy is always negative. For gravitational PE ,when an object is lifting up, it's work done is negative(opposite direction). so the change in work done is negative. On the...

I am interested in pursuing a career change to electrical engineering with the specific goal of working in the space industry. I have served 18 years in the US Army in a field that has nothing to do with engineering or any other technically oriented field. I am committed to four more years of...

Homework Statement A single gas molecule of inertia m is trapped in a box and travels back and forth with constant speed v between opposite walls A and B a distance l apart. At each collision with a wall, the molecule reverses direction without changing speed. Write algebraic expressions for...

Homework Statement Show that the largest possible change in the kinetic energy , ##\Delta E_{kin}##, of a particle of mass ##m## running into another particle of mass ##M## at rest in the lab coordinate system is \Delta E_{kin} = \frac{-4AE_{kin}}{(1+A)^{2}}, where ##A = \frac{M}{m}##...

Why won't water wave undergo a phase change of pi when it propagates to a fixed wall just like a pulse of string does.

Ice melting in a box has the water coming off it at a temp just above freezing until all the ice is gone. Are all phase change materials pretty much the same, with their immediate containment container exterior staying pretty much just above their phase change temp until all the PCM inside has...

Homework Statement If ##\bf{v}## is a vector and ##\alpha## is a covector, compute directly in coordinates that ##\sum a_{i}^{V}v^{i}_{V}=\sum a_{i}^{U}v^{j}_{U}##. What happens if ##\bf{w}## is another vector and one considers ##\sum v^{i}w^{i}##? Homework Equations The Attempt at a...

Homework Statement A 15 000kg loader traveling east at 20km/h turns south and travels at 25km/h. Calculate the change in the loader's a) kinetic energy b) linear momentum Homework Equations ΔKE= 1/2mvf^2 –1/2mvi^2 Δp= mv2 –mv1 m= 15000 vi = 20km/h = 5.56m/s vf= 25km/h = 6.94m/s The Attempt at...

Homework Statement Initially 5 grams of salt are dissolved in 20 liters of water. Brine with concentration of salt 2 grams of salt per lter is added at a rate of 3 liters per minute. The tank is mixed well and is drained at 3 liters a minute. How long does the process have to continue until...

Homework Statement A cylinder contains 0.250mol of carbon dioxide (CO2) gas at a temperature of 27.0∘C. The cylinder is provided with a frictionless piston, which maintains a constant pressure of 1.00atm on the gas. The gas is heated until its temperature increases to 127.0∘C. Assume that the...

Can we really reduce the compressor work by adding phase change material in evaporator. theoretically, it looks that it'll work but still confusion remains...

Good day everyone I'm doing a homework and stuck on the parts ii, iv and v. In fact I don't know the formula to calculate them Could someone help me to solve them, please

Hi I have a scenario with which I wish to understand . I have a ball on a string which is in uniform circular rotation at Tangential velocity v Assume friction is not present I now increase the centripetal force by pulling on the string from the centre, what has happened to the tangential...

In what follows I refer to the ideas of "Thermodynamic: Foundations and Applications" by Gyftoploulos and Beretta. The abbreviated form of my question is: In a reversible weight process, Ω1R-Ω2R = E1 - E2 (see eqn. 6.18, p. 99) is transferred out of the composite of a system A and a reservoir R...

Convert the following expressions to the indicated base using base 14 for a < 0 & a not equal to 1.$a^{5/\log_9a}$ So i been stuck for 1 hour trying to figure out this problem may anyone guide me please

Convert the Following expression to the indicated base, using base 14 for a > 0 & a \ne 1.[MATH]{a}^{\frac{5}{log}_{9{}^{a}}}[MATH]

Hi, everyone, I submitted a manuscript to Physics Letters B on about June, 10th. Then received the reply from the editor with two reviewers'comments on July, 15th. Reviewer #1 had some criticle comments on the theory which my paper was based on and gave some advise to me; Reviewer #2 had some...

For part of a proof of a differential equations equivalence, we needed to use that $$\int_0^t [\int_0^s g(\tau,\phi(\tau))\space d\tau]\space ds = \int_0^t [\int_\tau^t ds]\space g(\tau,\phi(\tau))\space d\tau$$ I understand that the order is being changed to integrate with respect to s first...

Why is it so that the net work done by a force on an object is equal to change in kinetic energy only and not any other form of energy like potential energy? Also is the work energy theorem valid for both conservative and non conservative forces.

With the change of variables-method for a many-to-one transformation function Y = t(X), what's the logic behind summing the different densities for the roots of x = t^-1(y)? Probabilities should be ok to add, but densities? Also, is there no way to extend this method for many-to-many...

I have two n-vectors e_1, e_2 which span a 2D subspace of R^n: V = span\{e_1,e_2\} The vectors e_1,e_2 are not necessarily orthogonal (but they are not parallel so we know its a 2D and not a 1D subspace). Now I also have a linear map: f: V \rightarrow W \\ f(v) = A v where A is a given n...