The tag has no usage guidance.

learn more… | top users | synonyms

3
votes
1answer
53 views

Distance between two galaxies of different redshift

Let $Q_1$ and $Q_2$ two different objects in the Universe (we can think to two galaxies or quasars), that we observe from the Earth at different angular position $(\alpha_1,\delta_1)$, ...
0
votes
1answer
37 views

Is displacement in circular motion a chord or an arc?

When taking the displacement between two points along a circular path to calculate its velocity, do you take the length of a chord connecting the two points or do you take the length of the arc ...
0
votes
1answer
29 views

Are measurements of time and distance independent or always coupled by the speed of light

In texts about special relativity the light clock is usually described as a tool to measure time $t$. It counts how often light travels along a given distance $d$, i.e. $t = d/c$, where $c$ is the ...
0
votes
1answer
52 views

How to use radio waves to calculate distance over short distances?

I read an article about a company that created the equivalent of a GPS location system for internal spaces where the satellite based GPS is blocked. They made reference to the Fresnel number as to ...
0
votes
1answer
33 views

Finding the distance between two osclilating particles in a wave

Assume a wave function $\psi = \psi(x,t)$ where $x$ is position from the starting point $(0,0)$ and $t$ is time. Two oscillating points A and B are located at $x_1$ and $x_2$ respectively with $x_2 ...
-1
votes
1answer
30 views

how can $r=\frac{1}{n^{\frac13}}$ be used to calculate the mean separation between electrons?

Can $r=\frac{1}{n^{\frac13}}$ be used to calculate mean separation of electrons suppose that Na which has BCC crystalline structure, each atom donate 1 electron to form metallic bonding As it's BCC ...
1
vote
0answers
28 views

Help with finding an equation to work out the length of cable required to produce loss of colour on an analogue video signal

When I briefly taught Broadcast Engineering I set up an experiment in order to demonstrate the effect of signal reflections along coaxial cable on an analogue PAL waveform. It involved getting the ...
1
vote
0answers
83 views

Which physical entities equal “distance times time”?

Are there useful physical quantities with dimensions of distance-time? The background for this question is a differential equation which I try to make sense of: ...
0
votes
0answers
49 views

Luminosity distance as a function of redshift

We know that the luminosity distance is: $d_L = a_0 R (1+z)$ with $z$ the redshift. How can we mathematically make explicit the dependence of $d_L$ from the redshift? I guess we need to make it ...
0
votes
0answers
58 views

measuring distances

We measure distances using half of the time of flight of light, 'a la Einstein'. What is the geometrical shape of the surface that is the locus of the points that are at a definite distance of an ...