Questions tagged [length]
The length tag has no usage guidance.
36
questions
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Uncertainty in length measurement
I am trying to measure the length and the uncertainty in length of a fiber optic cable for measuring the speed of light. So far, I have measured it the standard way: Using a standard meter scale. I ...
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1answer
63 views
Focal length for thick lens [closed]
How can I find the focal length of a thick lens by the method of ray tracing ? I know the ray matrix method but by ray tracing I don't get to an answer.
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1answer
32 views
Is cross-sectional area over length classified separately from length?
The ratio of cross-sectional area to length (or its reciprocal) appears in several formulas, including those for electrical resistance and capacitance in terms of the resistivity and permittivity. ...
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1answer
136 views
How length is an invariant in Euclidean space?
The special theory of relativity shows that intervals are invariant under Lorentz transform in the Minkowski space -time.
But how can we prove (any postulates or theory) that the length is an ...
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1answer
56 views
The length of a string attached to a wall?
I feel really dumb for asking this question. I apologize in advance.
When the example of a string attached to a wall is given to explain waves and the ressonance frequencies, the length of the string ...
5
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2answers
118 views
Is length an extensive property?
From my experience, volume, surface and length are extensive properties. Indeed :
the reunion of two cubes of 1 $m^3$ leads to a cube of 2 $m^3$
the reunion of two tiles of 1 $m^2$ leads to a tile ...
1
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1answer
96 views
Profile of a platinum-iridium meter bar
The former meter standard, platinum-iridium meter bar, had a specific cross section somewhat resembling mixed variant of letters "X" and "H" with serifs (Image source):
What was the reasoning behind ...
2
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1answer
59 views
Definition of a meter and Newtonian law of Gravity
Newtonian law of Gravity:
$$F_g = \frac{m_1 m_2}{l^2} G$$
$$G = 6.7 * 10^{-11} \frac{m^3}{kg * s^2}$$
A meter is defined as:
the length of the path traveled by light in a
vacuum in $1/...
0
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2answers
79 views
Lagrangian of a moving charge distribution under action of a eletromagnetic field
We all know that for a single charged particle, we can derive the Lagrangian starting from Lorentz law of force:
$$
\mathbf{F}=q(\mathbf{E}+\mathbf{v}\times\mathbf{B})
$$
and by using the ...
-2
votes
3answers
134 views
How to define approximate meter using primitive to no tools? [closed]
Imagine you've lost somewhere in the wild due to some catastrophic event, and don't have any measurement tools with you. How do you find approximate meter, millimeter, etc. with materials like sticks ...
0
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1answer
432 views
Relation Between Power, Distance, Time and Mass
I was calculating something and reached this equation
$${Meter^2 \over Second^3} = {Volt * Ampere \over Kg}$$
Is it correct? Cause if it is... It will tell me I am on the right path.
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3answers
384 views
Length contraction speed of light
The Special Theory of Relativity tells us that a moving object eg spaceship measures shorter in its direction of motion as its velocity increases.
At the speed of light it would have zero length, but ...
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4answers
2k views
What is superconducting coherence length?
I'm an electronics student, and don't know much about some physics concepts.
I was studying superconductivity and came to the London equation, Meissner effect and BCS theory.
I kind of understood ...
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1answer
128 views
If I cut a string, will its length be rational or irrational? [duplicate]
If I cut a string (lets say approximately halfway), will the length of each side (in inches) be rational or irrational?
2
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1answer
97 views
How to construct a 12-micron thin layer of powder+epoxy?
Okay, this is more of an engineering tactic question perhaps, but any insight into any possible process will be very, very appreciated. So I'm mixing a powder with epoxy, making a pasty, fluid semi-...
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1answer
73 views
Imperial to Metric lenght [closed]
I'm from Metric based country and have an unusual for me imperial notation.
Google didn't clear that up for me so I'm asking it here:
I have a wall with measures: 10'7-1/4''
What's 7 ? is it tenth of ...
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1answer
684 views
What is the spacetime unit?
So we have a graph of space vs. time, space being $y$, time being $x$. What's the unit for the distance between them?
$$\sqrt{(y m)^2+(x s)^2}$$
$$\sqrt{(3m)^2+(4s)^2}$$
$$\sqrt{\frac{(3m)^2}{(3 m)^...
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vote
1answer
23 views
Holograms - interference image, can I tell if the 2nd diode is good for holograms by comparing fringes?
I've created two fringe images - one of a laser diode that's able to make holograms which outputs 5mW.
The second laser outputs 20mW and so far I've not been able to make a hologram with it.
I had a ...
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1answer
170 views
relativity length contraction for twin clock experiment
The question im going to ask is based on scenario given here https://www.scientificamerican.com/article/how-does-relativity-theor/
Only thing that's different is that spacecraft has a length of 1 ...
2
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0answers
528 views
Bandwidth-length product of an optical fiber
A multimode step index fiber has a numerical aperture of 0.2 and a core refractive index of 1.47 . Estimate the bandwidth-length product for the fiber assuming only intermodal dispersion when:
(a)...
0
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1answer
130 views
A question about the definition of proper length
As I understand it, the proper length of an object is defined as the length of the object in its rest frame. In terms of the metric it is defined as the length of the spacetime interval between two ...
2
votes
1answer
409 views
How to read this length interval in imperial units?
I am from Europe and I do some research for my thesis. I found this picture, which is very usefull for me, but unfortunately the lengths are in imperial units (for lenght they are using something like ...
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1answer
70 views
How to calculate the diameter of a moving circle from afar while lacking and knowing some information?
Let's say there is a solid wood wheel with two tires attached at the bottom travelling on a level road towards me while facing me width-wise (as in, the side of it from which you can see its diameter)....
2
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1answer
109 views
Does limiting to infinity violate laws of physics?
It is noteworthy that one cannot simply divide any length more than the Planck-length. If so, one cannot simply divide any volume more than the $(Planck-length)^3$.
So if I want to find the limit of ...
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2answers
1k views
Why isn't a meter defined from a kilogram of water?
Why are there different official definitions for a kilogram and for a meter when a meter can be defined by the volume of a kilogram of water? For instance, using the triple point or some other state ...
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2answers
573 views
Can you express mass in other dimensional units?
I'm just started a Physics I course, and while I've paid attention, I'm stuck on one of the first problems:
Express mass ($M$) in terms of acceleration($a$), density($D$), area($A$), and time($t$).
...
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votes
3answers
16k views
Proof for Resistance is directly proportional to length and inversely proportional to the area of cross-section?
I have heard that Resistance is directly proportional to length and inversely proportional to area of cross-section. Can someone give me a practical explanation for this?
4
votes
2answers
145 views
where is the logical hole in this reasoning? (special relativity)
I cannot see the problem in the following reasoning, so I'd be glad if you could help me out.
The problem is defining a notion of "length" that is consistent with the constancy of the speed of light ...
2
votes
3answers
1k views
Proper length in GR
What meaning/use is associated with the notion of proper length in general relativity? Do you know an example of any quantity that depends on it? I have so far found statements like "the length ...
0
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1answer
549 views
What Is the Physics principle behind dropping a stone into a cup of water?
I have been doing an experiment about relationship between drop height of a stone and the loss of water in the cup it lands in. I found that after dropping the same stone into a cup with the same mass/...
7
votes
3answers
5k views
Can I calculate the size of a real object by just looking at the picture taken by a Camera?
Can I calculate the size of a real object by just looking at the picture taken by a Camera? (I think people do that) i dont understand how? (from physics point of view)
3
votes
2answers
201 views
How to theoretically define a concrete operation to perform in order to measure the length of an object?
EDIT: Some answerers pointed out that the title of this question is in contrast with what is actually been asked in the body of the question, so I changed the title accordingly.
The original title was ...
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3answers
165 views
Could this suggest that there is a wavelength smaller than Planck's?
Suppose the earth receives a photon with a wavelength $\gamma_1$. Since spacetime is expanding, we know that this photon had an original wavelength $\gamma_2$, such that $\gamma_2\lt\gamma_1$. This is ...
2
votes
2answers
3k views
Calculating the coherence length from a spectrum
I have measured the spectrum of the LED in my interferometry set-up, and now I want to calculate the coherence length from it. A commonly found formula is $l_{coh} = \frac{c}{\Delta f}$, sometimes ...
1
vote
1answer
352 views
Confused about length contraction and aberration [duplicate]
Einstein states that a moving object's shape changes due to the length contraction. But people had done such an experiment: Taking photos to a moving object, but they didn't find Lorentz contraction, ...
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0answers
47 views
Can a value of “length, in meters” be attributed to a pair of ends which are rigid (but not at rest) to each other? [duplicate]
The definition of the SI base unit "metre" [1] doesn't seem to rule out explicitly that a certain value of "length, in meters" could be attributed to a pair of ends which are rigid to each other, but ...
