Confused Definition and 1000 Threads

how could you calculate the input voltage at an input impedance from a voltage source? I saw they use voltage division law to find the voltage at the input impedance(Zin) from a voltage source(Vs). They do it like Vs * Zin/(Zin+Zs). The problem came... We all know that we can determine the...

hello i need some help and am confuse about it now.. after calculating the math.. 1.67531519 x 10 power of negative 8.. if i change to nano it is 16nf? 1.515761363 x 10 power of negative 10, if i change to nano is 15nf? what about changing to miro? confuse with the 10 power of...

There is several things I am confused about with gravitational potential energy. So, first of all, shouldn't U=mgh always be written ΔU=mgΔh, because isn't that equation only dealing with differences of potential energies when close to the surface of earth? Second, with the equation U=-GMm/r...

Homework Statement You have two charges, q1= -15uC and q2= 3uC, separated by a distance d= 3m. We want to calculate the electric field, E, at a location x relative to charge q2 located on a line connecting the two charges. Note that x could be anywhere on that line. Also need to calculate the...

Homework Statement Your weekly cost to manufacture x bicycles and y tricycles is C(x,y)=20,000+60x+20y+50√(xy) a. What is marginal cost of manufacturing a bicycle. b. What is the marginal cost of manufacturing a tricycle. c. What is the marginal cost of manufacturing a bicycle at...

Hi, I'm new both to this forum and to physics in general. Here's hoping I've posted in the right place... I'm basically trying to understand the difference between energy and matter and how one can become the other. Please bear with me, I'm a total layman and can't seem to get a definitive...

This is not a homework problem, but pertains to the class (Calculus II) that I am taking. I am very confused about how to think intuitively about determining orientation of a cross product. My understanding of the right hand rule in determining the orientation of the third axis is that...

So we are talking about velocity and acceleration, as well as the Kinetic Motion equations. Everyone is saying to make a chart, if you will, seeing which variables are present and which one you need. They say this will help you in picking an equation. However, I am still really having a hard...

Calculating laser fluence -- so confused Hi, I'm now endeavoring to calculate laser fluence using some laser parameters. The required parameters to solve the fluence are given as: Spot size: 10mm diameter Pulse duration: 200ms Repetition rate: 2-3 (Hz) Laser Power: 200mW (when...

Homework Statement Solid disk, 50cm in diameter, with a mass of 5kg. Disk is located in space by a bearing. The friction torque of the bearing is 10Nm. A string is wrapped around the disk and connected to a weight. The weight is allowed to fall and spin the disk. How much energy is lost to...

Homework Statement Find the maximum value of the function f(x, y) = x + y subject to the con- straint xy = 16, x > 0, y > 0. Homework Equations f(x, y) = x + y xy = 16 The Attempt at a Solution I attempted this first using substitution, then using LaGrange multipliers. Both...

so I'm fine with the kets, e.g, |a>.. but i don't understand what the bras are. the kets are basically just a column vector right? ie the components (with the direction) of the vector being described. but what is the bra? this was given to us in class: <a|=a1<e1|+a2<e2|= (a1* a2*) (where e1...

All commutative groups have one dimensional representation ##D(g_i)=1, \forall i## I understand what is representation. Also I know what is one, two... dimensional representation. But what is irreducible representation I do not understand. How you could have two dimensional irreducible...

Hi all, I think this is a self help question, but I still need some advice. I am a Post Graduate Mechanical Engineer and started a job from past 6 months. Initially I enjoyed Engineering because I liked to be with passionate people and building some things. In addition I enjoyed learning...

Tell me where I've gone wrong (here r(1,2) means position of point 1 with respect to point 2 etc): ω x r(1,2)=v(1,2) Differentiating both sides with respect to time: ω x v(1,2) + \alpha x r(1,2) = a(1,2) =>ω x (ω x r(1,2)) + \alpha x r(1,2) = a(1,2) Now let us imagine a uniform rod in free...

Homework Statement The question asks us to find the superposition of 2 waves where y1=3cos(4x-1.6t) and y2= 4sin(5x-2t) and find the superposition of the waves y1 + Y2 at x=1 and t =0.5 Homework Equations The Attempt at a Solution Okay, what confuses me. is my teacher explained...

Ok, so i by itself is -1, but i^2 is also -1, and I don't really understand why both are, and why we need i if it is just -1? Am I missing part of the definition?

Homework Statement The system consists of a 20-lb disk A, 4lb slender rod BC, and a 1-lb smooth collar C. If the disk rolls without slipping, determine the velocity of the collar at the instant theta=30 degrees. The system is released from rest when theta= 45 degrees. Homework Equations v=wr...

Sometimes when I see pulley and rope questions people will say "for a non-extensible rope the tension is uniform throughout the rope". But I am now learning pulleys and rotational inertia and it seems to be necessary to consider the rope on either side of a pulley to have _different_ tension if...

Confusion over the formation of cooper pairs Hi all, There are 2 points I do not get: 1. I read something saying that phonon is an energy packet of "heat and sound", and propagates through lattice vibration...so, I thought it is saying that phonon is emitted by one electron, then...

Hey I've been trying to make a basic animation which involves launching a spaceship from one planet to another. Both planets orbit at different rates from the star with fixed speeds. The spaceship also has a fixed speed from start to finish. What i don't understand is how you measure...

Hi, Take a look at this synthesis of aspirin. Because I am noob, please bare with me. On the top there you can see how the acetic anhydride gets attacked by the H plus ion. I can't understand why the h plus ion gets bonded there. I`ve been trying to find the answer to this question for...

This is probably going to be a very simple question, i just need justification for a seemingly simple step in a proof. The statement is as follows: An endomorphism T of an inner product space is {0} if and only if \langle b|T|a\rangle = 0 for all |a\rangle and |b\rangle. Now it is obvious if...

I am trying to design an optimal colormap for display interval data. I would like to create a scale that is linear in perceived luminance while adding a hue component to help mitigate the simultaneous contrast effect. However, I am confused on what hue to pick. The longest curved path I...

I have a question I'm having trouble with. A wire is stretched 1.2 mm by a force of 240n. Calculate the force needed to stretch the wire 2.0mm assuming the elastic limit is not exceeded. I'm new to physics and I have only used formulas for finding stress, strain and youngs modulas...

I have attachted the question as a picture: my first attempt i calculated the voltage through the auxillary circuit to be 10V but i am confused of where the 0.5 A plays in this part, then i used nodal analysis to find the voltage input to the amplifier but up to that point i am confused of...

Hello, I am confused about the terminology moment, specifically that there is a 1st moment and 2nd moment. What does moment even mean, and why does it have numbers associated with them?

Homework Statement How much photon energy would be required to produce a proton-antiproton pair? Where could such a high-energy photon come from? Homework Equations E^{2} = (pc)^{2} + (E_{0})^{2} The Attempt at a Solution Since the photon is massless its energy is E_{i}=pc The final...

Hello, in exercise 11, I get b is not and w is, but the answer key says b is and w is not...? I don't understand...have I misunderstood or is the answer key wrong? Regrds, $$|\pi\rangle$$

I've got this problem right now, which asks me to prove that $$Ccos(\omega_{o}t-\phi)=Asin(\omega_{o}t)+Bcos(\omega_{o}t)$$ This proved to be a bit more difficult than I expected, so I looked up a complete list of trig identities. $$cos(a\pm{b})=cos(a)cos(b)\mp{sin(a)sin(b)}$$ seems like the...

From WIKI, In February 2007, GRB 070201, a short gamma-ray burst, arrived at Earth from the direction of the Andromeda Galaxy, a nearby galaxy. The prevailing explanation of most short gamma-ray bursts is the merger of a neutron star with either a neutron star or black hole. LIGO reported a...

I don't get how you would attempt problems with 'tilted' projectile motion. So basically here's a situation: You are standing on top of a building, and throw a ball down the hill (hill is linear). Find where it lands Since you are standing on top a building, you have a Δy component...

I understand simple concepts, like \frac{dx}{dt}=v and why that is, but when I'm doing, for example, uniform charge distributions, I don't understand what the integral is actually doing. For example: E_x=∫dEcosθ From what I learned in calculus, the dE means with respect to. So when taking an...

So I was reading a thread on PF talking about the radius of a solenoid and Bob S answered with a link: On that site, it states that the Radius = the outer radius - the inner. It doesn't make sense. What happens when there is only one layer of coil and the outer radius (OR) is basically the...

If light takes 1 year to reach a destination, and it takes a ship 2 years to reach the same destination, how fast is the ship going? Is a question like this possible to answer without more information? I'm looking at the Lorentz transformations, and am finding all sorts of ways to be...

So dx means an infinitesimally small change in x. Why is the slope written \frac{dy}{dx} instead of \frac{f(x)}{dx} since you are only making the x component infinitely small? When you take the integral you do ∫f(x)dx not ∫dy*dx

Dear Forum members, I have a question regarding Special Relativity. I think its answer may be a simple and obvious one but as a complete physics amateur I cannot put my finger on it. Imagine a long train traveling east at half the speed of light relative to a 'stationary' observer. For...

Notation for Heisenberg Hamiltonian ## H_{exch}=-\sum_{i<j}2J_{i,j}\vec{S}_i \cdot \vec{S}_j ## where the sumation extends over all spins pair of the crystal lattice. Suppose we have chain with four sites and periodic boundary condition ## H_{exch}=-J_{1,2}\vec{S}_1 \cdot...

I am trying to make it computer a side of a right triangle here is my code? double x1-1, y1=5, x2=4, y2=7; side_1, side2, distance; side_1 - x2 - x1; side_2 = y2- y1; distance = sqrt(side_1*side_1 + side_2*side_2); printff(The distance between the two points...

I recently decided to message a girl that I like on Facebook. It went well; the best part was she was asking questions that would keep the conversation going. Then all of the sudden she just didn't reply. It's been about a week since we messaged and we haven't talked since. What is she trying to...

Disclaimer: This is not for any class. I have downloaded this book ( http://www.ck12.org/book/CK-12-Physics---Intermediate/ ) and am ( attempting to (: ) work through it on my own. I am going through the section on relative motion ( section 3.3 in the book ) and am confused by a portion. It...

I am very much weak to study the whole physics. Now I am on the verge of of physics board exam but totally got hanged with all these physics relations and formulas. How can I remember all these derivations of formulas, one which I wonder why these stuffs is useful in our life? Please can aybody...

hello, The Weyl tensor is: http://ars.els-cdn.com/content/image/1-s2.0-S0550321305002828-si53.gif In 2 dimensions , the Riemann tensor is (see MTW ex 14.2): Rabcd = K( gacgbd - gadgbc ) [R] Now the Weyl tensor must vanish in 2 dimensions. However, working with the g g = [-1 0 0...

I read recently, "It is a law of physics that light is strongest when it bends," Is this statement true, false or just confused in the way it is expressed? Thanks :-)

EDIT ADDED: I already got it! Thank you for your ideas! :D 1. Homework Statement If you drive an average velocity of -72.8 Km/h for 55 minutes to a position that is 28.5 KM north of Jollitown, in what position did you start your drive?I'm confused with this negative average velocity, please...

Hello, I am a bit confused about the length contraction formula. The formula is : l=lo*sqrt(1-u^2/c^2), where lo is the distance measured in a frame at rest with the moving object. Now I was looking at a problem where a spacecraft just as it touches the finish line (event 1) a message from...

I'm reading "Relativity: The Special and the General Theory" and I'm at the end of Chapter 9 & confused. If I understand correctly, this is what he has said so far (in my own words): Say that lightning strikes 2 points (A and B) on a railway embankment. To determine whether the two...

Homework Statement let f be a function t: lf(x)l≤lxl show that f is continious at 0The Attempt at a Solution it's easy to see that f(0)=0 now \forallE>0 \existsα>0 \forallx\inD: lxl<α => lf(x)-f(0)l<E now in the solution manual they just put it like this : since lxl<α implies...

The integral is in the attachment. Why is the indefinite integral not equal to... et(i - 1)/(i - 1) + C Because d/dt[et(i - 1)/(i - 1) + C] = et(i - 1)

I'm confused regarding the phase diagrams of binary systems. Let's suppose we mix 2 liquids, A and B at a given pressure P that won't change during the whole experiment. I raise the temperature until I observe that some of the mix of liquids vaporizes. What boggles me is that it seems I can...