The result of sampling the property of a system

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1answer
41 views

Can we directly measure vectors' quantities?

Can we perform some kind of experiment that will give us, for example, the $p_x$, $p_y$ and $p_z$ of a particle in a single measurement? I'm aware that they commute so one measurement will not ...
3
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2answers
134 views

How can we measure time?

If we cannot define a proper time (or synchronize clocks in different positions) in an inertial frame (independent with the theory of relativity), there seems to be no direct way to confirm the 2 ...
5
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5answers
448 views

Uncertainty principle with two photons

Imagine an experimental setup in which you have to measure the momentum and location of a particle. To measure it we know we will have to affect it, and the uncertainty principle would come into the ...
3
votes
1answer
81 views

Measuring Atomic Radius of a Noble Gas

How exactly can you measure the atomic radius of a noble gas such as Neon or Helium accurately? Would liquefaction help? I also heard that the aforementioned gases are the only common elements which ...
0
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0answers
22 views

Contact resistance copper-silver

I need to determine the contact resistance of a copper silver interface. The copper wire was soldered to the substrate using an IR-Laser. I was wondering if I can treat the entire system as a series ...
1
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2answers
125 views

How can Lorentz contraction be “directly” measured?

If one is watching a relativistic object of e.g. spherical shape, which emits enough light to be detectable, it will, despite being Lorentz contracted, appear of its natural shape, although rotated. ...
1
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1answer
60 views

How stellar aberration is measured?

A simple calculation shows that stellar aberration due orbital motion of earth is roughly 20 arcseconds. My questions are: Practically how this small value is measured? Does this value is in the ...
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2answers
69 views

Accelerometer validation trace

I am attempting to validate an accelerometer. I have a triaxial accelerometer and placed it on a wheel which goes at various frequencies from 1 to 3 Hz. Am I right in thinking that I would expect the ...
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2answers
77 views

How to use an accelerometer to correctly quantify the magnitude of vibrations

Consider the following setup, an accelerometer is placed inside a helicopter, measuring "g" values along 3 axes (x,y,z) every 10 ms (100 times a second), during a helicopter flight. If one, wants to ...
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4answers
123 views

Equations of graphs

I am doing a practical write up of an experiment I did. Here is a graph using the raw data I got. What is the general formula of this graph, and what do I need to do in order to make that into a ...
17
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1answer
951 views

Is the Uncertainty Principle valid for information about the past?

My layman understanding of the Uncertainty Principle is that you can't determine the both the position and momentum of a particle at the same point in time, because measuring one variable changes the ...
4
votes
2answers
372 views

What is the duration of a snap?

What is the duration of a snap (of the fingers)? When someone says, "it's ridiculously fast, it's like [snap]" - where [snap] is them snapping their fingers - they would normally mean it is ...
1
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1answer
89 views

Plasma Question: Expression for electron temperature in terms of the voltage of each prong of a triple Langmuir probe?

So I am trying to derive an expression for electron temperature based on the voltages on a triple Langmuir probe. I have pretty much been following the triple Langmuir probe derivation on wikipedia ...
0
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1answer
71 views

Combining ±% with ±dB in measurement uncertainty

Firstly apologies if this is not the correct place to post this but wasn't sure which site would be good to ask regarding about measurement uncertainty calculation. I am trying to calculate the ...
0
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0answers
22 views

Cosmic ray noise, strategic cancellation

With the radio telescopes, we measure the radio waves produced by every solar fluctuation in the near universe, which as I understand is heard similar to radio static we experience in tuning to a non ...
1
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0answers
71 views

How to specify BRDF measurement

As a person who will be using the scattering measurement results (in Zemax), I was asked to prepare the specs for the BRDF measurement. However I've never done it until now, so help would be greatly ...
0
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1answer
173 views

How to convert acceleration in g to speed velocity in meter /s [closed]

I'm working on an inertial measurement unit with some MEM'S component. I want to retrieve data on a micro-controller. I have 3-axis accelerometer sensor. however I want retrieve data in $mg$ ( ...
1
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1answer
183 views

Measurement using Vernier Callipers [closed]

The diameter of a cylinder is measured using a Vernier Callipers with no zero error. It is found that the zero of the Vernier scale lies between 5.10 cm and 5.15 cm of the main scale. The Vernier ...
0
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1answer
48 views

Significant figures in measurement with error

Someone can explain me what's the rule behind the correct expression of a quantity $K$ with its error $\Delta K$ as $K \pm \Delta K$? They must have the same number of significant figures? Or the ...
0
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1answer
59 views

Pendulum Confusion

This text in my book is pretty confusing:With my emphasis A simple pendulum is a heavy point mass (bob) suspended from a rigid support by a massless and inextensible string. This is an ideal case ...
0
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1answer
37 views

Probablilites for wave function collapse

From what I understand, superposition is when two states exist in all of their possible forms simultaneously until the moment of wave function collapse, when they essentially reduce into a single ...
2
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2answers
106 views

What can be measured or derived about a remote magnetic field? [closed]

This question related to Why are magnetic lines of force invisible? and is motivated by a comment of @BlackbodyBlacklight, based on that, the illustrating example may depend on that linked question as ...
3
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0answers
51 views

What is the shortest controllable time?

I was reading http://en.wikipedia.org/wiki/Planck_time and noticed a reference to: http://phys.org/news192909576.html where it is stated that: 12 attoseconds is the world record for shortest ...
2
votes
1answer
68 views

Probability of measuring two observables in a mixed state

Lets say i have density Matrix on the usual base $$ \rho = \left( \begin{array}{cccc} \frac{3}{14} & \frac{3}{14} & 0 & 0 \\ \frac{3}{14} & \frac{3}{14} & 0 & 0 \\ 0 & ...
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0answers
23 views

Is there a general term for the situation where an improperly chosen measurement range results in a bias?

For example, consider the following measurement: A sensor can measure a specific physical quantity, and has a range of $0$ to $100$. All values above $100$ will be shown as 100. We now take the ...
2
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5answers
254 views

What's the difference between $10\%$ of $10\text{ cm}$ and $1\text{ cm}$?

I overhead a physics professor at my university on the phone: I interviewed that student you sent me, but he didn't know the difference between increasing the length of a $10\text{ cm}$ rod by ...
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0answers
35 views

What can I say about compatibility between predictions and results?

If I have these theoretical predictions: \begin{align} \omega_{p_1} = 4.5132 \pm 0.0003~\text{rad/s} && \omega_{p_2} = 4.5145 \pm 0.0002~\text{rad/s}\\ \omega_{b_1} = 0.0707 \pm ...
1
vote
1answer
40 views

Small question about accuracy and precision

Let's say I have a law like this, $$D=\frac{c}{r}$$ where $c$ is a constant, $r$ a distance in meter. my measures of $r$ are [$0.02m$, $0.01m$], then $<r>=0.015m$ and $\delta r = \pm 0.005m$. So ...
0
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0answers
26 views

Local tension and pressure measurements

We want to measure tensions and pressures on the surface of a tooth for an experiment in dental research. We want to do local measurements at different points on the tooth. The tooth is not a real ...
1
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4answers
272 views

Can a thermometer really measure the temperature of a substance?

When we measure the temperature of a substance by using a thermometer and waiting until the two come into thermal equilibrium, the thermometer will not display the original temperature of the ...
2
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0answers
39 views

sensitive scale & resistance of analog current meter

Does the resistance of an analog current meter increase or decrease when it is set to a more sensitive scale (lower range)?
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10answers
319 views

Could one measure a stick to an arbitrary precision by having its length estimated by enough people?

I remember reading somewhere that the problem of exact time-keeping on ships could have been solved a lot earlier than it was if somebody would have had the idea of keeping time with a whole array of ...
2
votes
1answer
352 views

Non-Hermitian operator with real eigenvalues?

So we know that in Quantum Mechanics we require the operators to be Hermitian, so that their eigenvalues are real ($\in \mathbb{R}$) because they correspond to observables. What about a non-Hermitian ...
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0answers
41 views

Measuring CO2 concentration from a respiration chamber

I am interested in measuring the concentration of CO2 from an open circuit respiration chamber where a sheep is living. Known variables: Concentration of CO2 of the air entering the chamber. ...
0
votes
1answer
76 views

The value of one atomic mass unit

In my textbook, it is given: 1 atomic mass unit equals $1/12$th mass of one carbon 12-atom. Since mass of $6.02 * 10^{26}$ atoms of carbon-12 is $12\space\text{kg}$. Thus, $$1 \text{ a.m.u ...
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vote
2answers
156 views

Why does a microphone membrane only measure pressure and not particle velocity?

Microphones (e.g. condenser microphone) are assumed to have a voltage output proportional to the sound pressure at the diaphragm. If the operating principle is that the voltage output is proportional ...
2
votes
0answers
34 views

What is weak coupling of photon polarization to a pointer?

This question is refered to those who are familiar with the concept of weak measurement. In short: How can the polarization of a photon be coupled to the position of a pointer state? What is the ...
2
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0answers
45 views

How to formulate collapse in polarization subspace of a photon?

I am wondering how to describe the collapse of a photon state when it is measured in the polarization degree of freedom (say by a filter which let pass just one particular polarisation). Let the free ...
1
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1answer
96 views

Measuring a fluctuating quantity: Instrument error vs. uncertainty, or both?

Say I am measuring a quantity $x$ in physical system whose true value is approximately sinusoidal in time. I have an instrument to sample this quantity, for which the manufacturer gives an accuracy ...
0
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1answer
84 views

Blood Viscosity

When measuring blood viscosity, the literature claims that we generally use a cone-and-plate viscometer. Why is this; is there any way to explain this mathematically in terms of the shear rate, etc? ...
2
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0answers
51 views

need data-point: count rate of APD (avalanche photo-diode) for specific aperture and stellar magnitude

I hope lab / experimental physics is fair game for this web-site. If not, sorry! I'm designing a sensor system to perform specialized [astronomy and space-sciences] experiments, and need a "reality ...
0
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1answer
324 views

Effect of waters changing specific gravity on objects apparent weight placed in liquid

My goal is to monitor the change in specific gravity of a liquid over a period of time. My question is: What are the appropriate formula for determining expected apparent weight of an object immersed ...
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1answer
36 views

Error analysis and how values in references are determined

Question 1:Most science textbooks have appendixes that have a value for some physical property of some object. This includes diameter of electrons, viscosity of fluids, boiling points, etc. My ...
2
votes
2answers
212 views

Shouldn't the Uncertainty Principle be intuitively obvious, at least when talking about the position and momentum of an object?

Please forgive me if I'm wrong, as I have no formal physics training (apart from some in high school and personal reading), but there's something about Heisenberg's Uncertainty Principle that strikes ...
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5answers
93 views

Addition according to significant digits

I have been studying about significant digits and addition rules and I can't quite digest the rules of addition completely. It states that in the answer number of decimal places will be equal to the ...
3
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2answers
159 views

Significant figures vs. absolute error

On NIST Avogadro's Number, $N_A = 6.022\;141\;29 \times 10^{23} \text{ mol}^{-1}$ has 9 significant figures and a standard uncertainty of $0.000\;000\;27 \times 10^{23} \text{ mol}^{-1}$. First, can ...
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1answer
83 views

How does laser induced fluorescence in excited atoms work?

Atomic clocks use laser induced fluorescence in order to detect excited atoms, how does this work? Apparently the clocks need to detect the states of nearly 100% of the atoms being examined. In an ...
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1answer
49 views

Rotation speed measurment

Could anyone please explain with simply how we can measure the rotation speed of an object using the Sagnac Interferometer ?
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1answer
234 views

Is it possible to use induction ampermeter to measure power consumption of electric water heater and dryer?

I hope this practical question is not OT and not too trivial for this forum. I am renting an apartment in a duplex with a shared water heater and dryer. Turns out, both water heater and the dryer are ...
2
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2answers
283 views

Accuracy and Error of Atomic Clocks

I'm quoting a passage from my notes: The development of clocks based on atomic oscillations allowed measures of timing with accuracy on the order of $1$ part in $10^{14}$, corresponding to errors ...