# Tagged Questions

19 views

### How many measurements of a physical quantity should you do to get a representative value / distribution? [on hold]

When we measure a physical quantity multiple times, we can calculate several values which should help us understand the whole measurement better: Standard deviation, variance, median, average, and so ...
26 views

### What does a MEMS gyro measure during off-axis rotations?

I've been working with MEMS gyroscopes in hobbyist projects for years—but it's recently come to my attention that I don't have any principled understanding of what rotation rate measurements ...
51 views

### Can we measure rates in real time?

I know what it means to say that my position is "X" at a particular moment in time. I can easily take a picture of my motion and observe my exact location at the instant the picture was taken. That is ...
41 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 ...
75 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 ...
246 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 ...
76 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 ...
42 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 ...
84 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 ...
54 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& ...
114 views

### How do you measure proton's spin? [duplicate]

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 ...
183 views

### Measure mass difference of an object without a scale

For a project i need to separate items based on their mass in real time. I like to explore measuring weight of an object (round metal ball) by taking photographs (several) during free fall and ...
406 views

### Doesn't the use of a thermometer alter the temperature of the system?

If I place a mercury thermometer in hot water, heat energy will transfer from the water to the mercury inside the thermometer. Will this continue until thermal equilibrium is reached and thus the ...
130 views

### Is there a fundamental limit to the temporal resolution of signals from space?

In Earth-based experiments, we can measure phenomenon very rapidly in an experiment given appropriate equipment. Clearly if something takes a long exposure to see (due to a weak signal), then the ...
151 views

### Need to weigh a sack of kittens

Hypothetical brain teaser here, no real kittens involved! - For some bizarre reason I have a sack of kittens, I need to find the total weight of the kittens and the sack but I'm only allowed to use ...
2k views

### Radius of curvature of lens: Newtons Ring method vs spherometer

I have to do an experiment to find out the radius of curvature of a lens using the Newtons ring method given that you know the wavelength of the monochromatic light used in the experiment. What the ...
214 views

### GHz rate single photon counting

The fluorescent lifetimes of molecules used in biological applications tend to be in the sub-ns to a few ns timescale (let's say 0.8-4). The most direct methods to measure lifetimes typically involve ...
738 views

### Can we measure an electromagnetic field?

As far as I can check, the Aharonov-Bohm effect is not -- contrary to what is claimed in the historical paper -- a demonstration that the vector potential $A$ has an intrinsic existence in quantum ...
715 views

### How hot is the water in the pot?

Question: How hot is the water in the pot? More precisely speaking, how can I get a temperature of the water as a function of time a priori? Background & My attempt: Recently I started spend ...
1k views

### Uncertainty in Acceleration given the uncertainty in position

I had a motion detector record the position of a dynamics cart and automatically plot Position vs Time and Velocity vs Time plots in Logger Pro on the computer. If the instrument uncertainty in ...
137 views

### Experimental perspective in understanding the Heisenberg Uncertainty Principle

I need to confirm whether or not I understand Heisenberg Uncertainty Principle. So the crucial thing is that you need an "ensemble" of measurements: $$\delta x \delta p \ge \frac{\hbar}{2}.$$ If I ...
118 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 ...
424 views

### Photometer: measured Irradiance L converted to photon rate

I am conducting an experiment in which the power meter reading of $410\,nm$ narrow bandpass stimulus is noted to be 30 $\frac{\mu W}{cm^2}$ at a distance of 1 inch away from the light source. I wish ...
314 views

### experimental technique for measuring temperature of an ant

I am taking a course on thermodynamics. I have a question from my text(halliday & resnick,physics-1). They asked me to measure temperature of an ant or an insect or a small body,like a small ...
124 views

### Basic question about probability and measurements

Say I have a Galton box, i.e. a ball dropping on a row of solid bodies. Now I want to calculate the probability distribution of the movement of the ball based on the properties of the body (case A). ...
485 views

### Weinberg angle measurement methods

I was reading up on the history of $W/Z$ bosons today and I got a little puzzled. I always assumed that people measured $M_Z$ and $M_W$ and then derived the Weinberg angle. But it appears that they ...
227 views

### How do I do error calculus right using gnuplot as an example?

Given is a set of measurements with their respective errors for example an energy spectrum. In gnuplot one is to fit a function $f(x;\{p_i\})$ depending on a variable $x$ and on fit parameters $p_i$. ...
131 views

### Good algorithm for in-experiment 1-D optimization?

I'm running an experiment -- for the question, it doesn't matter which one, but I'm measuring an optical intensity $I$ as a function of two parameters: reflection angle $\theta$ and wavelength ...
72 views

### Are a measured object always part of the theory?

Is there a notion of measurement, which doesn't correspond to a yes/no question or with the idea of the comparison of two real world objects, which produces a real number? And does at least one of ...
64 views

### How to properly read a measurement result if it is a number?

If the result of a measurement is i.e. $3.2 \pm 0.7$, what is 0.7? At which confidence level we know that the real result is inside of this interval?
2k views

### How did they measure the speed of light observing Jupiter's moons, centuries ago?

I am interested in the pratical method and I like to discover if it is cheap enough to be done as an experiment in a high school. Thank you.
24 views

### Review of Gas Chromatographs?

Could anyone suggest a recent review article or book on gas chromatography instrumentation? My interest is in the devices themselves, rather than using them for a particular application. This ...
343 views

### How can I measure the physical properties of a metallic string?

Metallic strings exist in different kinds but I would like to measure for a metallic string: the section/geometry along its length, to a precision of 1/100 mm its elongation when a tension is ...