Doubt Definition and 580 Threads

Hello! Homework Statement It is more a conceptual problem. If all the variables are known, and I am asked to write x as a function of time, why the equations below are not equivalent when equation (b) is derived from (a) after substituting "v_f = v_i + at" ? (a) x_f = x_i + 1/2(v_f + v_...

Hi, I have some silly doubts and i read some articles about FFT but could not able to conclude my self. What are the difference between 1) FFT power sprectrum and Power sprectrum density 2) FFT Phase and magnitude 3) FFT Real and imaginary Can some make it clear to me.

Doubt about relativity! I am a noob! Forgive me if it sounds too stupid! Let me say, I am in CERN right now at the LHC. I fire a proton at 0.9c in one direction. While this happens, I also fire another proton at 0.5c in the opposite direction. Both the measurements were done considering...

https://www.physicsforums.com/showthread.php?t=253563 There is this post on this theorem. But the issue I wanted to discuss isn't discussed there fully(so far as I could follow the thread). So I am creating this thread for that issue, so as to avoid necro-post in that thread. My doubt is...

I have sensor that produces differential output. I saw in the sensor schematic that they have used 2.5v DC as reference in the output minus terminal. I am taking sensor output as differential that both positive and negative(2.5DC ref terminal)in count. I got output as 1v of DC when the sensor is...

I am just reading an op-amp datasheet. In that, they have written in features as "RAIL-TO-RAIL OUTPUT SWING" and in Applications as "MULTI-CHANNEL DATA ACQUISITION". What does they mean? Can someone explain me in simple way.

The other day I happened to open an ammeter just out of curiosity. What I saw was that across the positive and negative terminals a wire of considerable thickness(almost equal to the thickness of wires we use for household joints) was wound..It just had 4 or 5 turns. I guess it should be the...

Hi, Question: X and Y are two identical sources of sound which emit in phase. Calculate the lowest possible value of frequency of the sources for there to be (a) constructive (b) destructive interference at Q. So, X is at 1.8 m from Q and Y is 1.2 m away from Q. a) If they leave in...

Hello people! Well, I am doing some excercises for fun. Picked some Precalculus stuff, and found this excercise: "Construct a function that has the same slope at x = 1 and x = 2. Then find two points where y = x^4 - 2x^2 has the same tangent line (draw the graph)." I have found a solution, but...

On the provided attachment, I have problem understanding the last step of the 1st sum of that page. Can anyone explain to me what is being done after the second-last step?

Hi everyone, Maybe it could be an idiot question but I've never know why. If centripetal force points to the center, Why a car making a turn tend to skid to away of the road? I mean, there would have to be a force opposite to centripetal, that is in fact, greater than it, for the...

Hi This question is taken from the book Classical mechanics by Gregory. Please clear this doubt TIA ------------- Suppose that a reference frame fixed to the Earth is exactly inertial. Which of the following are then inertial frames ? A frame fixed to a motor car which is (i) moving...

Hello, my name is Dennis; and I am rookie engineer. I have a doubt in the above circuit and I was wondering if any of you could help me. I have attached a schematic for a power/ battery charger circuit. Right now My concern is on the battery charger circuit marked with a red box. According to...

No, not doubt as in questioning the capabilities or fact of the matter (as connoted in the western usage), but doubt as in general uncertainty / question (as I see from many Indian / Pakistani users, and grad students around my department!) Maybe this is just confirmation bias, but I notice a...

" Depletion Layer is the region in diode which consists of ions( formed due to formation of octet configuration )of p-type and n-type dopants" What happens to the ions present in the depletion layer when a diode is biased? why the depletion layer width changes??

Homework Statement In feedback problems of amplifiers we often use H feedback in the voltage controlled voltage sources... The good thing about that is that they are connected in series parallel form and they are then to find the net h parameters we simply add the h parameters of the...

Will someone please explain the foll. doubts in this solved problem from David Morin's book. TIA sree ------------ DOUBTS : 1. What is the principle of eqn. 3.78 ? If V is block speed and Vy is its component in y dirn., why should V + Vy be constant ? 2. In Why should...

I have a doubt that I cannot resolve: With a 10kg stop object on a surface I apply a 100 N force to move this object. The static friction coefficient is 0.5 and kinetic coefficient is 0.3. I would like to know the maximum speed of this object and the distanced covered till stop. I know the...

given the function arg\xi(1/2+is) is this an increasing function of 's' ?? , i mean if its derivative is always bigger than 0 here xi is the Riemann Xi function http://en.wikipedia.org/wiki/Riemann_Xi_function could we define the 'inverse' (at least for positive s) of...

well if i understand relative motion quite well but while thinking about it i had this doubt- if A is in center of circle and if B is rotating in that circle, A would see B rotating rite? now , how would B see A?... there are more questions to follow up based on the answer...

Friends, A doubt in piezoelectricity. I heard that when pressure is applied in a quartz crystals(or other similar items), a high voltage is produced and this is called piezoelectricity. My question is, is it necessary a pressure cycle should go on? i.e. first a high pressure, then low, then...

Attached is a worked problem in the Classical Mech book by Morin. I don't understand how eqn (2.57) is the net moment about the pivot. Isn't it only the moment of the weight of the portion of the stick to the right of the pivot ? What about the moment due to the weight of length 'l' on left...

The usual derivation of the wave form equations from the GR field equations is done in the weak field, linearized approximation of the GR theory. In this limit, that ignores non-linear contributions and that gives accurate results when used to predict solutions for problems in the Newtonian...

I have been working on programming and trying to learn fast all the things. I have some doubts about following logics that when to use and where. Please explain me in short and undestandble way. 1) when to use exactly AND, OR and reamining logic functions. 2) when to use arthimatic and...

Doubt on Inductor!pleasez help Imagine an AC source and a pure inductor...if the Instantaneous EMF=Back EMF due to changing Magnetic field in Inductor then how does the current flow?

This doubt is about a text in Peskin Schroeder Pg 86. I reproduce it here. -------------------------------- U(t,t') satisfies the same differential equation (4.18), i \frac{\partial}{\partial t} U(t,t') = H_I(t) U(t,t') but now with the initial condition U=1 for t=t'. From this...

Latest results from the LHC are casting doubt on the theory of supersymmetry http://www.scientificamerican.com/article.cfm?id=beautiful-theory-collides "I'm wouldn't say I'm concerned," says John Ellis, a theorist at CERN, Europe's particle-physics lab near Geneva, who has worked on...

Homework Statement Hi there. I'm not sure if this question corresponds to this subforum, but I think you must be more familiarized with it. The thing is I don't know how to get from: M_x=(I_0-I)\dot\Psi^2\sin\theta\cos\theta+I_0\dot\Phi\dot\Psi\sin\theta to...

I had a thought going in my head today about the uncertainty principle. Forgive me if it sounds too silly. Consider an electron in motion. Now, suppose that I'm measuring it's position with infinite accuracy. So, by the uncertainty principle, it's velocity is blurry. But what if I measure the...

A small doubt in transformer... Hi friends A transformer (say step up one) increases the output voltage. However, power input is equal to power output so output current should be small. Now yesterday I took a spark circuit(from an electric gas lighter using a 3 volt battery) and allowed the...

Hi... I was reading through the second edition of the book Galactic Dynamics from Binney and Tremaine. Chapter 3 :eqns 3.8 and 3.9. 3.8 says r^2 \frac{d \phi}{dt}=L=constant. Then 3.9 writes \frac{d}{dt}=\frac{L}{r^2}\frac{d}{d\phi} But is this correct? For example, if I act this on r...

Hi everyone, Homework Statement I've been studying a paper in which there is a connection given by, A = f(r)\sigma_1 dx+g(r)\sigma_2 dy, where \sigma's are half the Pauli matrices. I need to calculate the field strength, F = dA +[A,A]. Homework Equations A = f(r)\sigma_1...

Hi everyone, I've been studying a paper in which there is a connection given by, A = f(r)\sigma_1 dx+g(r)\sigma_2 dy, where \sigma's are half the Pauli matrices. I need to calculate the field strength, F = dA +[A,A]. I have computed it, but a factor is given me problems. I would say, dA =...

Hi everyone! I'm studying Laurent Series, and I thought I understood it but after solving one exercises I get confused. The problem was to get the Laurent series for the following function: \frac{1}{\left(z-1\right)^2\left(z+3\right)} I do it this way: \frac{1}{\left(z-1\right)^2}\cdot...

Hi, I am new to circuit design. Although, I am designing CSA&SA(charge sensitive @ shaping amplifier) for our detector system to detect the radon gas emission. We soldered every thing and we observe the output that is bit noisy. I learned some concepts in my course about...

what is planar technology?

Hi, basically i am confused about the characteristricts of silicon diodes and waffers. As i know the VI @ CV characterstricts of the diode. But i tested the same characterstricts with silicon waffers which behaves perfectly same as like diodes. Mainly i need to know about the difference between...

Hi, basically i am confused about the characteristricts of silicon diodes and waffers. As i know the VI @ CV characterstricts of the diode. But i tested the same characterstricts with silicon waffers which behaves perfectly same as like diodes. Mainly i need to know about the difference between...

Hello We all see this statement everywhere : "Planck's quantum theory states that the radiant energy emitted or absorbed by a body is in the form of discreet packets of energy called Quanta, and the energy of the quantum depends on the frequency by the formula E = hv" Now, my question is...

In an RC circuit shown below, with the switch closed after a long time, when the capacitor is charging, there is a current across the capacitor given by Initial current x e ^ (-t/RC)... Is this current...the current supplied by capacitor to the rest of circuit, or simply the current across...

Homework Statement is the drag on an airplane dependent on its weight? Homework Equations The Attempt at a Solution it was told that the drag depends on lift and the lift,on weight,in turn.but i am unable to comprehend it physically.

Lets say we have a function of a complex variable z , f(z). I read that for the function to be differentiable at a point z0 , the CR equations are a necessary condition but not a sufficient condition. Can someone give me an example where the CR equations hold but the function is not...

Hello friends Fourier law of heat conduction states that: Q ~ A.(Dt/Dx) where A= area normal to direction of heat flow. Dt/Dx= temp gradient in same direction. Now, obviously rate of heat flow will depend upon temp gradient but my doubt is how/why...

A vector space is a collection of vectors. So can we say that it is a set (although with special properties) ? Just wanted to confirm this. Is this also true for a vector space consisting of all functions from R to R , i.e can we say that it is also a set , where each member of the set is a...

Hello :D The block over block questions today got on my mind And i got some doubts in which i need some guidance :) Let the two blocks as shown http://s1102.photobucket.com/albums/g448/vissh/?action=view&current=LOM.jpg" . I want to find the accelerations of blocks when :- <1>F = 20 N <2>F...

Hi Everyone, I have very fundamental question on Acceleration. I can understand that a moving body accelerates or de-accelerate when its velocity goes up and down. But I couldn't understand; when we say a moving body accelrates or de-accelerates when the direction of moving body changes(with...

Homework Statement Hi. I have a doubt with this exercise. I'm not sure about what it asks me to do, when it asks me for the curvilinear integral. The exercise says: Calculate the next curvilinear integral: \displaystyle\int_{C}^{}(x^2-2xy)dx+(y^2-2xy)dy, C the arc of parabola y=x^2 which...

Hi all 30 students have sent me their answers to me in folders, "name1", "name2", ..., "name30". Each folder contains 2 outputs, "output_a.txt" and "output_b.txt" Now I have the correct answer "correct_a.txt" and "correct_b.txt" with me. I know that using the command diff, I can compare...

I have just started a study of linear algebra and I have a doubt regarding vector spaces. Consider the vector space spanned by the 3 dimensional vectors [1,0,0] and [0,1,0] , this would be a 2-dimensional vector space no doubt.But it also is a subspace of \mathbb R ^3.I have no problem in...

Homework Statement The problem statement has been attached with this post. Homework Equations I considered u = ux i + uy j and unit normal n = nx i + ny j. The Attempt at a Solution I used gauss' divergence theorem. Then it came as integral [(dux/dx) d(omega)] + integral...