Measurement Definition and 1000 Threads

I'm supposed to be working with an STM in the coming weeks to determining the Fermi Level of some semiconductor diamond films. I was bombarded with a lot of information by my lab supervisor and the bit of my notes about the calculation just says "Differential of voltage vs current allows us...

I recommend the following paper by Robert B. Griffiths on developing the theory of quantum mechanics without giving a special role to measurements: http://arxiv.org/pdf/quant-ph/0612065v1.pdf In my opinion, it does not answer all the questions about locality and realism that come up in...

Hi I saw something in Wikipedia and I am confused. I saw something like this 2.0 cm -/+ 0.05 cm Whats that mean? My first opinion Between 1,5 and 2,5 My second opinion 1,5 cm or 2,5 cm

like for example digital unit measurement for clear images in devices is ...pixel

Hello, If I have a measurement of 1cm, and have an absolute error of 0.1 cm, I know that I can write my measurement as (1±0.1)cm. If I want to write it with its relative error instead of an absolute error, can I still use the bracket? i.e) (1±10%)cm ? Thank you!

I need to collect data via measuring EMG signals in the upper arm. I have standard AgCl stick-on ECG electrodes. My question is, if I can use normal alligator clip cables for collecting this signal from the electrode and feed it into an instru-amp? Will this affect the signal strength and/or...

Hi. I have a problem understanding a question for my electronic engineering course. We have a subject that's directly translated to 'the knowledge of electricity and measurement techniques'. I do hope this is the correct forum to ask for help at. Homework Statement Given the...

Can someone recommend (if possible) a way to detect the amount of helium in a given enclosed space? I'm designing an experiment in which I will need to measure the amount in an otherwise vacuum.

Thanks for the answers on my previous thread, it made some sense, and if I'll reply if there's further misconception. My new question is quite connected to the famous Andromeda paradox. So it's stated that the Andromeda is far away and moving towards the galaxy will cause the observer to have...

Homework Statement Suppose the angular wavefunction is ##\propto (\sqrt{2} cos(\theta) + sin (\theta) e^{-i\phi} - sin (\theta) e^{i\phi})##, find possible results of measurement of: (a) ##\hat {L^2}## (b)##\hat {L_z}## and their respective probabilities. Homework Equations...

If we have a qubit in a mixed state, let say 1/2(+><+)+1/2(-><-) and we measure it. Is then the result a pure state + or - ? If this is the case, then the entropy of the system decreases. Now the question another way round is : Suppose we measure a quantum system without gaining...

According to "Physics for Engineers and Scientists by Ohanian and Markert, a second is the time needed for 9,192,631,770 vibrations of a cesium atom. In 1971, Hafele and Keating put four cesium-beam atomic clocks aboard commercial air liners which were flown around the world - two eastward...

Hello friends, Most people that I heard put uncertainty as an intrinsic property of the universe which is evident when we make a measurement. But to me it seems that intrinsic property and making a measurement are two entirely different things. If uncertainty were to be just(purely)...

Propose this measurement: It is a well know interference measurement, but now asymmetrical. Suppose the red path is 1 m and the blue path 10 m. If you measure the time between detector 1 and 2 I expect you will find two times: 3.3 ns and 33 ns. Then you know which path the photon took...

Homework Statement Given the wave function psi(x,0) = 3/5 sqrt(2/L) sin(xpi/L) + 4/5 sqrt(2/L) sin(5xpi/L) in an infinite potential well from 0 to L, what is the expectation value <x> and rms spread delta E = sqrt(<E^2>-<E>^2) Homework Equations <x> = integral from 0 to L of psi*xpsi dx...

So this semester our lecture explained and showed us the double slit experiment. And it he explained to us the uncertainty principal that the act of observation can change the result. However this is the part where I kind of a have a problem with.. Since quantum physics is based on the...

Halo everyone. I am new to here! I am working with a project of ocean wave energy. I would like have a device that can measure the wave length, pitch those wave parameter when I testing my wave energy device. Anyone have a clue what kind of device can complete my task?

Homework Statement Given the following wave function for hydrogen: psi(r, t=0) = (1/sqrt(10))*(2*psi_100 - psi_210 + sqrt(2)*psi_211 + sqrt(3)*psi_21(-1)) where the subscripts show n, l, m_z, respectively, and the psi_nlm_z are already normalized. - At t=0, we measure and find l = 1...

How does the Copenhagen interpretation motivate its claim that the wave function of a quantum system collapses when a property of the system is being measured? I mean, was there some problem they were trying to solve by introducing the notion of wave function collapse? What would happen if the...

It is often said that non-commuting observables cannot be simultaneously and precisely measured. The rough idea is that the procedures to measure each observable are different. Is the statement strictly correct? If so, what is the mathematical argument? Is it possible to use Ozawa's...

I have a couple of questions about what total harmonic distortion is, and what the measurement means. The definition I've read most places is: \frac{D}{S} × 100% , where S is the amplitude of the fundamental frequency, and D is the amplitude of the sum of all of the harmonics. A common...

Hi All, I would like to know why the neon lamp is used to measure electrical polarity. What is the working mechanism involved. Best wishes, DaTario

Here's what I'm thinking. The sun is too bright to measure directly with our equipment. If I calibrate without a filter, and capture the reference spectrum with and without the filter, then I can model how the filter changes the spectrum. This way I can capture the sun spectrum with the filter...

Hi, I know the common proof of the no-cloning theorem assuming the cloning apparatus acts unitarily on the system and leading this to a contradiction. But what about a non-unitarian apparatus that involves measurements? I'm pretty sure cloning is still impossible, but I don't know how to...

Homework Statement Two sources, A and B, emit a sound of a certain wavelength. The sound emitted from both sources is detected at a point away from the sources. The sound from souce A is a distance d from the observation point, whereas the sound from source B has to travel a distance of...

Hi, I was just writing another thread when I stumbled upon something strange: What if I now make a slight change and replace ##\bf{b}\rightarrow-\bf{b}##? The expectation values containing ##\bf{b}## change signs and I get $$\left|\frac{1}{\sqrt{2}}-0\right|=\frac{1}{\sqrt{2}}\leq...

Hi, I'm trying get a better understanding of Bell's inequality in the form $$\left|E\left(\bf{a},\bf{b}\right) -E\left(\bf{a},\bf{c}\right)\right|\leq 1+E\left(\bf{b},\bf{c}\right)\enspace.$$ I'm considering the Bell state $$\left|\psi\right\rangle=...

Hello, I was wondering if anyone can recommend any good articles or journals with valid and good velocity data for flow from an impinging jet on a flat surface with an approximate Reynolds number of around 75,000 to 90,000? I have looked and seem to have lots of data for heat coefficients but...

If we entangle particles and separate them by a large distance, can the action of measuring one cause decoherence at the other's location? If yes then does this violate relativisitic causality? Could we not use this process to transmit information instantaneously? If no then why not? Is there...

Hello, I don't seem to know how to ask google this question so I thought I'd see if I could get an answer from here. Say I have 400 measurements of some variable. I take a sliding window of 50 events and take the standard deviation of each set of 50 events. That would be 350 measurements. Now...

Hi PF people, I am brand new to PF and this is my first post so please excuse and help correct any mistakes I make. My question is about time, the perception of time and the units we measure it in. I figured I would start this question with a statement because if my general understanding of...

I have just completed an experiment on principles of lasing, constructing a laser and measuring the beams intensity distribution. This distribution of the beam was measured using a detector mounted on a traveling microscope. The detector had a pinhole cover such that only a small fraction of the...

Hey guys, I know you all wish you never had to do all the weird conversions required for our current system of measurement. I know I'd rather convert 17km to m than 17mi to feet or ever inches. I thought that since I know so many people who would rather just do the easy metric conversions...

Hello, If I want to measure the concentricity of a cylinder with another, is it possible using a CMM? If yes, can you pl. explain me the procedure? I have read that concnetricity has to be measured based on the mid point of a diameter-line of a cylinder. This means, I have to measure the...

Hello PF members! First of all, let me start off my post by admitting that I have created a duplicate account. My original account was banned for a good reason. Now, I am studying physics. More specifically, I'm studying relativity. I trust that you all will help me understand what...

Hi, I have a question about how to interpret the state of an entangled photon H = horisontal, V = vertical polarization The global state is |Phi> = (|H>|V> + |V>|H>)/sqrt2. By density operator formalism: rho = |Phi><Phi| = (1/2) ( |H>|V><H|<V| + |H>|V><V|<H| + |V>|H><H|<V|...

Morning everyone, We know of some illusions in our everyday experience, such as an echo making us believe someone is talking back at us, or mirages in the desert, or mirrors making us think there are two symmetric objects when one is only the reflection of another. I was wondering about...

How can I measure the power associated with a vertical rotating shaft (similar to the shaft of a vertical axis wind turbine). power=Torque*angular velocity Angular velocity can be found by using tacho meter or spectroscope.. but i am confused how to measure the torque...

Do gyroscopes give the angular rates about its local axes or about a frame that is fixed and initially coincides with its local frame? I mean: would this sensor give the rate of change of the Euler's angles or the angular velocity ω (about the inertial frame)? One more question: I know that...

Im not sure if there are any implications to be made, but it struck me as interesting as what would happen if measurements of the same parameter were simultaneously made on each of two entangled particles? Can anyone speak to this perchance?

How do astronomers measure cosmic distance, say 7 billion light-years? http://www.space.com/17399-gamma-ray-photons-quantum-spacetime.html

First I am trying to find the theoretical flow rate but I am not able to get the answer because since diameter of the pipe is 0.03m throughout, when I sub into the formula: My A1/A2 will be 1, and 1-1 = 0. And I will get maths error whatever is divided by 0. Am I going in the wrong direction...

I always try to assume that pretty much anything I think of has been thought of before, so I am relatively sure that this is also not a new question. we base our current measurement systems on arbitrary lengths such as the meter or foot, etc. there are certain applications where we use...

what is differences between collapse,reduction, decoherence , weak projection and strong projection in quantum measurement theories?

hi I read this statement in site www.askamathematician.com and I couldn't understand it. is it possible to explain this? "if measurements A and B are taken enough apart, they will be “space-like separated” according to SR, meaning that neither event precedes the other. Some observers will...

Sorry if I'm in the wrong subforum. This is a rather simple and straightforward question, I hope. I'm doing a measurement that requires me to do a linear regression on data points to get a value of the slope. The slope is the value of the actual property that I am measuring. Assuming...

I want to ask a question regarding how spin state of an electron becomes entangled with the slit an electron travels through in the double slit experiment. So I understand that in the double slit experiment, we have two slits 1 and 2. We place a detector by slit 1 to measure whether or not...

Hi, I'm doing some research on developing a physics-based platform game and I want to see how the gameplay will feel if the environment and physics were made to scale as realistically as possible. Since one of the core features of a 2D platformer is jumping, I need some figures on how much...

Suppose we have x plates of wood of thickness (0.0150 \pm 0.0002) \text{ m} and we wish to stack them into a pile of height (1.000 \pm 0.001) \text{ m}. The number of plates x required is then x = \dfrac {1.000 \pm 0.001}{0.0150 \pm 0.0002} \, . How many plates will certainly fit in the...

why am I only getting 16v between both line phases coming into my service from the meter on a 240v single phase panel for a home