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 ...
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  • 70.2k
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 +...
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  • 221k
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 ...
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  • 1,059
22 votes
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Which experiment gave scientists reason to believe nuclear fission/fusion produced energy?

which experiment gave scientists the reason to believe nuclear fission/fussion existed Fusion was first. Francis William Aston built a mass spectrometer in 1919 and measured the masses of various ...
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  • 16k
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 ...
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  • 19.3k
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 ...
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18 votes

Sun spectroscopy - Home experiment

The resolving power of a prism is given by the formula $$ \frac{\lambda}{\Delta \lambda} = b\ \frac{dn}{d\lambda},$$ where $b$ is the base length of the prism, $\lambda$ is the wavelength and $n(\...
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  • 110k
17 votes
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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 ...
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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. ...
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15 votes
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How do I find the right lens for my laser?

You can't do this with a single "normal" lens. Because the beam width needs to be 4.25 inches you need a lens wider than that (which is huge compared to normal optical components). The focal length ...
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  • 860
15 votes
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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 ...
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  • 110k
15 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 ...
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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-...
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  • 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 ...
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  • 4,960
12 votes
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How do we perform transverse measurements in a two level system?

You do exactly the same thing: you "rotate" the state and then measure along whatever axis your measurement apparatus happens to measure. The only difference here is that the "rotation" does not ...
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12 votes
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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 ...
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12 votes
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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. ...
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  • 221k
11 votes
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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 ...
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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 ...
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  • 759
10 votes

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 ...
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10 votes
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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, ...
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9 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 ...
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  • 116k
9 votes
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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 ...
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  • 283
8 votes
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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 ...
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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 ...
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  • 11.3k
7 votes
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How to make sure that two electrons collide head to head?

Short answer: you don't. Slightly longer answer: You're using beams of particles, and you focus each of them as much as you (practically1) can so that the particles in each beam are reasonably close ...
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7 votes
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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 ...
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  • 473
7 votes
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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 ...
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  • 1,921
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 ...
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  • 32k
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 ...
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