Measurements Definition and 382 Threads

Homework Statement We needed to measure the temperature of a bucket of water using a thermometer which can be read to 0.1°C. Each group would do a single measurement, the data from five groups (including our own) was to be averaged with the uncertainty stated. The data collected was: 19.5...

I was wondering if it would be possible to determine if a Schottky diode was n-type of p-type (in the bulk) by only using I-V measurements?

Hey guys, I'm very new to quantum mechanics and have purchased 'Quantum Mechanics: The Theoretical Minimum. I'm still a bit confused by a fairly fundamental idea. In the book, it states that you first prepare a spin state (say the σz = +1) in the initial measurement. If you rotate the...

For example, I weigh a pebble and get a value of 7.1g. Then I measure again and get 7.6g, then again and get 6.9g.. Then I repeat the measurement using the same scale 5000 times. (its just a thought experiment). Is the mean of all measurements closer to the true value and if so, why? thanks

I was wondering, since the Earth is constantly moving around the sun, the sun is moving around the milky way, and the milky way is moving through space (and for all I know the milky way might also be rotating around our local group, cluster, super cluster, etc.), how do we know how fast...

I'm having trouble with error propagation analysis. When you make a single measurement of several variables, say (x,y,z) and you calculate a function f(x,y,z), you just have to apply the common formula of error propagation: $$\sigma_f(x,y,z)=\sqrt{\left| \frac{\partial f}{\partial x} \right|...

I can get a measurement of my distance between points (x1,y1,z1 and x2,y2,z2) by analysing position data from a GPS/barometer system, which has a standard deviation of about 2m for x y z positions. I can also analyse data from a system that provides velocity with a standard deviation of about...

Homework Statement Consider a particle with orbital momentum ##l=1## and spin ##s = 1/2## to be in the state described by $$\Psi = \frac{1}{\sqrt{5}}| 1,1\rangle|\downarrow\rangle+\frac{2}{\sqrt{5}}|1,0\rangle|\uparrow\rangle$$ If the total angular momentum is measured what would be the...

Hello,just seeing if someone can help me on here,i have a rc glider measuring 2200 mm on the ground,when in the air it measures about 35mm. Can the the height be calculated from these measurements.

In the story I am currently working on, a weapon commonly used on ships is a sort of coilgun. I want to create a ratings system for these coilguns and want to know the range of ampule-turns that would be used in large coilguns (barrel diameters range from six inches to two feet).

Hello, I have some questions on uncertainties in measurement: Say you have a ruler with 1mm graduations, and you are trying to measure the length of a metal rod. One end of the metal rod is at the 120.0mm graduation, and the other is in between the 19 and 20mm graduation, and you approximate...

I am confused about very fundamental question. Why does the rms value of number of electrons collected from a signal(like in photoconductor) gives you the noise in that signal.

Here I criticize the whole concept of weak measurements and weak values in quantum mechanics, first proposed by Aharonov, Albert and Vaidman: http://prola.aps.org/abstract/PRL/v60/i14/p1351_1 1. By a suitable choice of the post-selected state, the weak value can be made ARBITRARILY large. In...

Hi All, So here is an error analysis question for you all: I am measuring the temperature of an object at three positions simultaneously. They are type K thermocouples so their individual error is 0.75% of their reading. However, I can also take long term data which shows that...

Hello everyone! So I am currently working on a project involving classroom equipment from PASCO. (http://www.pasco.com/prodCatalog/WA/WA-9314_microwave-optics-basic-system/#overviewTab) What I'm working on is not exactly related to the the classroom project but closely related to the...

How would you figure a problem like this- 9' - 6 11/16 +17' - 9 3/4 I'm trying to reteach my self this math, and I can't remember how this is done. Please help asap!

In ARPES measurements, people say that the laser light cannot cover a wide area of momentum space whereas the synchrotron light can (M. Hashimoto et al., Nat. Phys. 10 (2014) 483). Why is that? (Figure 3a in the paper is a combination of laser and synchrotron data to plot spectra along the...

Hello All, I'm working on a design for a board that will allow me to plug in a standard 10x scope probe and then reduce and isolate the signal to go into the input of an ADC in a microcontroller (0-5V range) with a max bandwidth of 100 kHz. I have been shopping around for a while looking at...

Hey everyone.I have a couple of question regarding wave function collapse. I can accept that one cannot make a measurement with absolute precision and have a usable wave function afterwards due to the uncertainty principle... Consider a particle moving along the x-axis with a wave function...

I'll be cautious in asking my my question because I'm out of familiar territory. But... Given the following: that dark matter interacts with baryonic matter (exclusively?) via gravity, that evidence for dark matter shows that it exists largely near baryonic matter, and we are (almost?)...

Hello, I am having a problem about the nature of the measurements of the intervals ds's forming out of infinitesimal displacements dx's of the coordinates and the actual meaning of the measurements of the same dx's, in flat metric spaces. I am certain that this must be a trivial problem...

Here is my theory: - The measurement of an observable by an observer is a thermodynamically irreversible process. All thermodynamically irreversible processes increase total system entropy. - Landauer's principle (which was experimentally shown in 2012) says that the minimum amount of energy...

Ive attached the R ratio formula to this post, please could someone who is familiar with it tell me what Nc is? Does it relate at all to centre of mass energy? Thanks in advance for any help. source...

Homework Statement Which of the following best summarizes how a photoelectric detector provides an energy measurement: Answer choices: A) As light of multiple colors falls on the detector, the detector measures the energy of just one frequency of light by having a hole of only one...

Hello, I have been working for a while in weak measurements and I have noticed that some physicists such as Aharonov, Vaidmenn or Popescu have suggested that weak measurements reveal some sort of retro causation phenomena. One of the things that confuse me is that they state that when we weakly...

There is an argument that accurate sequential measurement of conjugate observables A and B on the same state is possible if the state is an eigenstate of one of the observables. When the state is an eigenstate of A, an accurate measurement of A will not disturb the state, so B can then be...

Hello everyone, the forum looks great and I have been reading it for a long time, but I have only registered. I am writing this post because I have to analyse two flow fields in a wind tunnel. 1) The first flow is generated from a helicopter blade, with Re=2000000, Mach=0.92 and...

This is a hard to explain question. If what I wrote makes no sense to you please let me know so that I can fix it. Suppose a zone where the weather changes like a Markov chain between sunny, cloudy and rainy. You can't observe it directly, but you have a sensor that gives some information...

Hello everyone, I have a large number of measurements with associated uncertainties, and I know that the real values are bounded above by some constant. How can I estimate the value of that constant, and the uncertainty on the estimate? Thanks

http://www.space.com...map-aas223.html Recent measurements suggest the universe it is flat and infinite The new results, presented by Schlegel and his colleagues here today (Jan. 8) at the 223rd meeting of the American Astronomical Society, also provide one of the best-ever determinations...

Hi, Assume we have a source that emits several copies of the same quantum state which is a superposition of several eigenstates of the Hamilton operator with different energies. We can calculate the expectation value of the energy of this state and therefore also the energy the source...

I don't know much about physics but just had this idea: As I understand it the HUP prevents good accuracy of a small object's momentum and position at the same time. Assume trying to measure the momentum and position of a single atom. In theory, can't we get a very good idea of both of...

In another thread WannabeNewton mentioned: and gave this reference: Until WBN mentioned it, I had never given any thought to the difference between these methods of measuring rotation, so I would like to explore those ideas further here, particularly in relation to the Kerr metric. Consider...

Advanced Project -- Wheatstone Bridge for TCR measurements Ok, so I have to do this experiment on my own as part of my coursework this year and I picked something called the temperature coefficient of resistance. I think I basically have to determine the TCR or copper and I'm almost...

Homework Statement I have 3 data points of steady state temperature at 3 locations some distance away from a bulb, I need to calculate the temperature of the surface of the bulb. It would be best to assume the bulb is a hemispherical radiation source, based on the experiment set-up...

Hi, This isn't my field at all so please excuse my ignorance. Let's say I have a pipe positioned at 30 degrees to the horizontal and an inclinometer attached to the pipe in a vertical position. Now I rotate the pipe some amount about it's long axis. The inclinometer reads 15 (or...

I am curious about a question. in synchrotron station,people use x ray to do kinds of experiments. They use the x ray ,how do they know the characteristic(like wavelength,brightness) of the ray they use. Does they measure the x ray when they use it simultaneously? Does this have an bad effect on...

Lets say a sensor measures within accuracy of +/- 0.05N And you take multiple measurements and graph it out. (I.e., 5.12N, 5.15N, 5.05N...). What is the uncertainty of the final average? One way I read is: Sx = s/√N where s = std. dev. N = number of data points But...

I am using a extended Kalman filter for the state estimation of a nonlinear system. The real system has accelerometers, so I need to include the acceleration of the system as part of my measurements with noise added (position and angular rates are other measurements). All of the Kalman...

I was thinking about units and started wondering about coupling constants. In unit-independent form, the fine-structure constant is defined as \alpha = \frac{k_e e^2}{\hbar c} I don't have a deep knowledge of particle physics but I know that there are weak and strong charges which enter the...

There is a statement in the Landau and Lifgarbagez volume on quantum mechanics that has had me puzzled for weeks now. They say (bottom of pg. 23): "If the electron was in the state psi_n [an eigenstate of f], then a measurement of the quantity f carred out on it leads with certainty to the...

I am trying to measure the relative permeability of a few materials, but the numbers I'm getting don't quite make sense. Maybe someone here can figure out what might be going wrong. My setup is as follows. I'm making solenoids using 30 AWG magnet wire wrapped around ferrite, steel and wood...

In the use of the word "causation" can one say that one quantum state "causes" another if the two states are not measured? Or does the concept of causation only refer to a relationship between measurements?

I am just starting out in self-study for quantum theory, so forgive me if my question seems elementary or completely misguided. In quantum mechanics, every wave function ψ can be decomposed into a linear combination of basis functions in the following manner: \Psi = \Sigma{c_{n}\Psi_{n}}...

This is a pretty basic question I believe. When you describe the state of a single particle, let's say its spin state, it can be in a superposition of different states (like up and down). When you do a measurement of its spin you'll either get up or down, since its spin state will collapse into...

It follows from the Expectation value postulate that an observable A, associated with the operator A^, can be precisely measured only if the wave function ψ of the system is an eigenfunction of A^ . Accordingly, the position and momentum of a particle can never be precisely measured because...

Hi, say I measure something ten times and get x+d1x, x+dx2, ... where dx1, dx2.. are the measurement errors. Now, say I want to calculate something from these measurements according to: A = B(C(x)), Where A is what I want, and B and C are known functions. Which is statistically...

Ok so I'm currently revising my quantum theory course from this year and I've reached the section on the postulates for measurements in quantum mechanics. The one I'm having trouble with is "The only result of a precise measurement of some observable A is one of the eigenvalues of the...

Hi Folks, I somehow cannot get the difference and have to admit that I am left confused. For a probability of measuring m with the operator M on state \Psi_i p(m|i) = <\Psi_i| M^{+}_m M_m |\Psi_i> = <\Psi_i| M_m |\Psi_i>. The average of an observable is defined as <O> = <\Psi_i| O...

Metric holds an advantage in simplicity, but imperial seems to have better unit amounts. For instance, temperature. I cannot think in celcius. 60's weather is 15-20 celcius. 70's is 20-26 celcius. 80's weather is 27-34 celcius. Lengths: a mile is a significant accomplishment for human...