The result of sampling the property of a system

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2
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4answers
188 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 ...
1
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0answers
26 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 ...
0
votes
1answer
64 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 ...
1
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1answer
45 views

What is the appropriate device for measuring energy loss from collision with surface?

The surface of a running track (i.e. cinder or rubber) has an effect on a runner's performance. I would like to get some device for measuring how much energy a runner loses on each surfaces. I've ...
2
votes
1answer
105 views

Is this the correct way to I combine multiple interdependant pressure readings?

I want to measure the density in different layers of a suspension. To do this I want to place pressure sensors at different heights. Let's assume that the sensors are not by orders of magnitude more ...
0
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0answers
22 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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1answer
28 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 ...
1
vote
4answers
100 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 ...
9
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10answers
262 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
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0answers
12 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)?
2
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1answer
89 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 ...
1
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0answers
8 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. ...
1
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1answer
48 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 ...
0
votes
1answer
46 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 ...
6
votes
2answers
153 views

Mean of a measurement on periodic data: what is the use of the inverse of correlation length?

Correlation and autocorrelation is something that in my Bachelor's programme in physics has been somewhat overlooked, so I'm in trouble understanding their use in this paper (The prisoner’s dilemma on ...
2
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1answer
74 views

How is the energy of a lightning calculated?

I was wondering how is the energy of a lightning measured? Is it based on the luminous intensity and/or the generated sound? What about the generated heat and energy spent in the production of ozone? ...
1
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1answer
46 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 ...
0
votes
1answer
175 views

In terms of covariance matrices, are partial measurement and partial trace equivalent?

Partial measurement and partial trace There is a connection between a measurement of a part of a system and tracing this subsystem out. Say, we have a system composed of subsystems $A$ and $B$ in a ...
2
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0answers
24 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
31 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 ...
0
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1answer
43 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
votes
1answer
43 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
28 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 ...
2
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2answers
88 views

Are negativity of the Wigner function and quantum behaviour equivalent?

I've read the following question: Negative probabilities in quantum physics and I'm not sure I understand all the details about my actual question. I think mine is more direct. It is known that the ...
0
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1answer
53 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 ...
2
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2answers
124 views

Which is smallest distance measurement which makes sense talking about [duplicate]

This might seem a silly question, but here it goes: Of all possible values for a measure of distance, which is the smallest that makes sense talking about? I mean, I could talk about $10^{-100000}$ ...
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1answer
24 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
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2answers
101 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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2answers
33 views

Measuring radon level

In theory what are the techniques used to measure the levels of radon in air? On which principle/law do they rely?
2
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5answers
68 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
3k views

How to combine the error of two independent measurements of the same quantity?

I have measured $k_1$ and $k_2$ in two measurements and then I calculated $\Delta k_1$ and $\Delta k_2$. Now I want to calculate $k$ and $\Delta k$. $k$ is just the mean of $k_1$ and $k_2$. I thought ...
2
votes
2answers
70 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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0answers
31 views

Rotation speed measurment

Could anyone please explain with simply how we can measure the rotation speed of an object using the Sagnac Interferometer ?
2
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2answers
125 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 ...
0
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2answers
106 views

How to estimate a person's mass from a sensor? [closed]

I'm trying to estimate the person's weight from some available sensors and I have an accelerometer, a gyrometer and a magnetometer. The triaxial accelerometer is fixed in a band in the person's ...
0
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2answers
44 views

Can stress be observed directly?

Strain can be directly observed using e.g. a ruler. Can (internal) stress be directly observed?
0
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1answer
33 views

Charge or Charges on the oil droplets?

Due to my poor understanding of various paper and other material provided by google on Millikan's oil drop experiment I ask the following question here. As the drops were charged by either friction ...
6
votes
1answer
139 views

Is it feasible to measure the energy of cosmic ray muons with a consumer Digital Single Lens Reflex camera?

I have read this article SIBBERNSEN, Kendra. Catching Cosmic Rays with a DSLR. Astronomy Education Review, 2010, 9: 010111. and it talks about estimating the muon cosmic ray flux by means of a DSLR ...
3
votes
1answer
85 views

How to measure the mass of the electron?

I've done a little bit of research and it seems Millikan was able to measure the ratio between the charge of the electron and its mass. But how can one measure one of the two constants to get the ...
4
votes
2answers
84 views

How does QFT help with defining measurement in Quantum Mechanics?

I learned that a quantum system has an "overall state", a vector in a Hilbert space. That Hilbert space can be decomposed in a basis of "basic states". For example if in the Universe there is only a ...
0
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1answer
27 views

Resampling spectral data?

I want to use the CIE CMFs (Color Matching Functions) provided here: http://www.cvrl.org/cmfs.htm With data from my spectrometer in 10 nm increments. However, the CMFs are only provided at 5 nm ...
1
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0answers
53 views

Weighted average whenever a variance is 0? [closed]

So I have data for the number of times a certain event happens. Each column is a different event and each row is one trial. A sample of data would look like \begin{bmatrix} 1& 4& 7& ...
1
vote
1answer
56 views

Why is the angle of a triangular prism equal to the result of the following 2 calculations? (Experiment with optical goniometer)

I know there are two ways of measuring the angle of a prism with a goniometer: let the collimator shine (monochromatic) light on 2 sides of the prism and measure the angle between the 2 reflected ...
0
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0answers
23 views

How to estimate a final error when you have N experiments with N errors? [duplicate]

if we have Xo±e1, X1±e2, X2±e3, ..., Xn±en when we know these, what is going to be our estimation for X, and it's error? for example if we have 344±1, 350±2, 345±5, 338 ± 2 estimation? error of ...
1
vote
1answer
116 views

Expectation values in QFT?

What is the meaning of different expectation values in QFT? For instance: $$\langle 0|{\cal O}(0)|q,s\rangle$$ or $$\langle 0|{\cal O}(0)|0\rangle$$ with ${\cal O}$ being some operator and ...
2
votes
1answer
54 views

Uncertainty on a single observable measurement

Heisenberg Uncertainty Principle states (in the form of the Robertson-Schroedinger Formula) that measurement of two non-commuting observables has a limiting precision, even for flawless measurement ...
1
vote
1answer
79 views

Obtaining a measurement very indirectly [closed]

While answering a question I came to reflect on the fact that in science experimental setups measure things indirectly. Example: the setup of the Pound-Rebka experiment. The amount of absorption was ...
2
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2answers
98 views

How do you measure proton's spin?

I've probably read it somewhere in Sakurai but I cannot recall it at the moment. So how does one really measure the proton's spin? I mean the proton's spin and not its constituents. Do you measure ...
2
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3answers
120 views

Physics Standard Deviation

I am a physics enthusiast and I have a question: Why is it meaningless to express the '$\pm$' (standard deviation) value as a percentage?
78
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23answers
7k views

How can you weigh your own head in an accurate way?

I read some methods but they're not accurate. They use the Archimedes principle and they assume uniform body density which of course is far from true. Others are silly like this one: Take a knife ...