41
votes
What's the problem with my Young slits experiment?
The angle between maxima in the double-slit pattern is
$$
\theta \approx \frac\lambda d
$$
for wavelength $\lambda$ and slit separation $d$. I wild-guess that the slits in your photograph are about 5 ...
rob♦
- 85.2k
35
votes
Given fluids expand non-linearly, how were physicists able to make a linear temperature scale?
There are physics answers to your question.
To answer your worry at the level of the thermometer scale we see in our house thermometers, where the temperature is given equal intervals from -30C to +...
- 232k
23
votes
Given fluids expand non-linearly, how were physicists able to make a linear temperature scale?
Simplistically, you can always define a linear temperature scale. For instance, you could call the freezing and boiling points of water (at some standard pressure) 0 and 100 and then construct a ...
- 1,287
22
votes
Is there any advantage in stacking multiple images vs a single long exposure?
Stacking is something that is done all the time in infrared astronomy. This is done because CCD technology doesn't work for wavelengths in the range of roughly 2 to 10 microns, and beyond, so they use ...
- 22.2k
22
votes
Accepted
How is time measured in particle experiments?
The Higgs is a challenging example because the tabulated quantity is the decay width $\Gamma$, from which a mean life $t≈\hbar/\Gamma$ is inferred. That is, nobody starts a clock when the Higgs is ...
rob♦
- 85.2k
20
votes
Given fluids expand non-linearly, how were physicists able to make a linear temperature scale?
There are already great answers, but I would like to address how one could operationally define temperature.
As Tony already pointed out, we define a temperature scale that is linear. The scale ...
- 9,318
17
votes
Accepted
How to fix a bad KF flange?
I have fixed flanges like this by sanding. If your flange is aluminum, this won't be too hard; if it's stainless, it might be fairly tedious and painful!
Start with a coarse-grit sandpaper, around ...
- 383
16
votes
Is there any advantage in stacking multiple images vs a single long exposure?
The voice of bitter experience, here, to tell you about a problem that a properly working observatory shouldn't have to worry about. But I did the time I was working on a "serious" astronomy project.
...
15
votes
Accepted
Is there any advantage in stacking multiple images vs a single long exposure?
If your exposures are short enough (a fraction of a second), you can even combat turbulence in the atmosphere. The trick is to do very many short images then pick the ones where a (bright) point ...
- 126k
14
votes
How can we 'see'/measure/detect particles during experiments?
In short: The Physicists analyse the final particles in the decay chain and derive from them the properties of the interesting particles.
More detailed:
The particle detectors consist of various sub-...
- 183
14
votes
Given fluids expand non-linearly, how were physicists able to make a linear temperature scale?
The temperature scale we use nowadays is not based on thermal expansion of liquids or any other property of a substance which varies monotonically with temperature. Different types thermometers such ...
- 5,178
14
votes
One-way speed of light experiment, no clocks or mirrors (with simulation)
Unfortunately, there is simply no possible way to measure the speed of light independently of your synchronization convention. In this case, if you use the standard isotropic synchronization ...
- 92k
14
votes
Accepted
Experimentally Measuring the Velocity of Water coming out of an Orifice
Water is incompressible. So you can put a bucket under your stream and let it run for some time. That way you measure the volume of water coming out per time [units m$^3/$s]. Divide by the cross-...
- 6,424
13
votes
Accepted
Measuring the effective mass
The method I'll describe is called Cyclotron Resonance, and it's a neat way to directly measure $m^*$ by using a fixed magnetic field $\boldsymbol B$.
The equation of motion of the electrons in a ...
13
votes
How is time measured in particle experiments?
The shortest lifetime that was directly measured is that of the neutral pion, or $\pi^0$, the lightest meson at a mass of $m=135\,\textrm{MeV}$. It decays to (predominantly) two photons and it has a ...
- 1,289
12
votes
Accepted
How can we 'see'/measure/detect particles during experiments?
This answer is to be read in parallel with the one by Gnorkx.
This is one of the most recent particle detectors, CMS:
CMS detector in a cavern 100 m underground at CERN's Large Hadron Collider.
...
- 232k
12
votes
Accepted
What are the "x" marks in a bubble chamber image?
They’re “stereo fiducials”: marks used to calibrate from the distances on the (somewhat deformable film image) to accurate 3D positions during the scanning process. On the chambers I'm familiar with, ...
- 14.4k
11
votes
Accepted
Laser beam alignment: best practices
Safe Alignment
Since you're using visible wavelengths, you can align everything looking at it through webcams. They're so cheap and they see very well for many applications out to 11oonm. Put them ...
- 87.5k
11
votes
Accepted
Why do scientists need to measure extremely small intervals of time?
It all depends on the phenomena one is studying. If you need to make an analysis about the general pick up of a car engine, i.e. how much time it take to go from 0 to 100 Km/h, one does not need to ...
10
votes
Is there any advantage in stacking multiple images vs a single long exposure?
I haven't done this for astronomy, but have used an astronomy CCD down a microscope for electroluminescence and have also used cooled imaging CCDs for spectroscopy. Although I have often set the ...
- 774
10
votes
How are photons told apart by a PET scanner?
Scatter is indeed a big problem. We try to deduce whether detected photons are scattered by measuring their energy. With a modern PET detector, energy resolutions on the order of 12% FWHM (full width ...
- 118k
9
votes
Accepted
How do non-mechanical solid-state optical switches work?
It looks like there are at least two ways to go about this:
Bistable MEMS
MEMS (Microelectromechanical systems) are very small structures, with features from $1-100\mu m$ in size, generally made with ...
- 283
8
votes
Accepted
Why squared mass difference between neutrino 3 and 2 is a absolute value?
The experiments we've done so far are sensitive to the difference of the squares of the masses $\Delta m_{ij}^2 = m_i^2 - m_j^2$, not the square of the differences $\left( m_i - m_j \right)^2$. As ...
8
votes
How to fix a bad KF flange?
I can think of three possible fixes:
1) The easiest "work-around" involves using a teflon gasket. Teflon is known to cold flow and conform to the shape that it is clamped between. With sufficient ...
- 12k
7
votes
Accepted
Measuring air density - where is my huge error coming from?
Your method is the problem,
Imagine for an instant trying to measure the density of helium by the same method, your balance would measure a negative weight (the balloon rise), and hence a negative ...
- 473
7
votes
Accepted
Identifying the Higgs boson at LHC
In particle physics (as with most sciences) we are rarely ever concerned with analysing single events. What we look at are distributions of the same measurement(s) made many times. From performing ...
- 1,952
7
votes
Is there any advantage in stacking multiple images vs a single long exposure?
I don't know about astronomy, but one reason it can be useful in normal photography is to combat camera shake by auto-aligning the images before blending them. This can be useful if you want to take a ...
- 33.5k
7
votes
How is speed measured in the LHC
If protons in the LHC weren't obeying special relativity, then the accelerator wouldn't work at all.
In the LHC, protons are injected into the ring in "bunches" of a few hundred billion each, with an ...
- 35.2k
6
votes
Measuring the effective mass
Another method to measure the effective mass would be to measure the frequency dependent conductivity and the Hall resistance of a sample. Following Drude theory we can get an expression for the ...
- 1,784
6
votes
Accepted
Why does a CfBe neutron source not exist?
The very flexibility that you mention in your post is a bit of a problem in an experimental context. In order to understand the signal that a Cf-Be calibration source would generate in your detector ...
Only top scored, non community-wiki answers of a minimum length are eligible