A vacuum is a space devoid of matter. The word is derived from the Latin adjective vacuus for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often discuss ideal test results that would occur in a perfect vacuum, which they sometimes simply call "vacuum" or free space, and use the term partial vacuum to refer to an actual imperfect vacuum as one might have in a laboratory or in space. In engineering and applied physics on the other hand, vacuum refers to any space in which the pressure is considerably lower than atmospheric pressure. The Latin term in vacuo is used to describe an object that is surrounded by a vacuum.
The quality of a partial vacuum refers to how closely it approaches a perfect vacuum. Other things equal, lower gas pressure means higher-quality vacuum. For example, a typical vacuum cleaner produces enough suction to reduce air pressure by around 20%. But higher-quality vacuums are possible. Ultra-high vacuum chambers, common in chemistry, physics, and engineering, operate below one trillionth (10−12) of atmospheric pressure (100 nPa), and can reach around 100 particles/cm3. Outer space is an even higher-quality vacuum, with the equivalent of just a few hydrogen atoms per cubic meter on average in intergalactic space.Vacuum has been a frequent topic of philosophical debate since ancient Greek times, but was not studied empirically until the 17th century. Evangelista Torricelli produced the first laboratory vacuum in 1643, and other experimental techniques were developed as a result of his theories of atmospheric pressure. A Torricellian vacuum is created by filling a tall glass container closed at one end with mercury, and then inverting it in a bowl to contain the mercury (see below).Vacuum became a valuable industrial tool in the 20th century with the introduction of incandescent light bulbs and vacuum tubes, and a wide array of vacuum technologies has since become available. The development of human spaceflight has raised interest in the impact of vacuum on human health, and on life forms in general.
Hi All,
I was just watching the video on the Veritassium channel about scientific dissemination of general relativity. And I could see once again that when you try to use animations and/or computer graphics to show the transition from free space geodesics to geodesics around a planet, what you...
According to Maxwell’s Equations, the speed an EM plane wave in free space, far from its source, is determined by the electric constant, ε0, and the magnetic constant, μ0, such that c = 1/√( ε0 μ0).
The units of ε0 are capacitance per unit length and the units of μ0 are inductance per unit...
I've always had difficulty grasping why the electric and magnetic fields are in phase in EM waves in a vacuum. Of course, Maxwell's Equations imply that is the case, but I had a hard time intuitively visualizing it. Then I found this short video on YouTube. I would appreciate your opinion...
I am trying to draw the Poynting vector field for a single electron in free space between two capacitor plates. The electron is moving (and accelerating) to the positive plate at the right. I expected the Poynting vector field lines to converge to the electron, because that is where the work...
Lets go through the example problem until we get to the part I don't understand. Figure 25-17 can be used as a reference to all questions. From part (a) to part (b) we eventually find the charge q on one plate (and by default the charge -q on the other). No problem there. The battery is then...
If I'm trying to solve the problem of a particle in free space (H = P2/2m ).
the eigenfunctions of the Hamiltonian cannot be normalized.
now assume I have a legitimate wave function expressed in terms of the eigenfunction of H and I want to measure its energy.
what will happen to the...
the answer is 2.16*10^-11
what i don' t understand about the question is why did they not use the constant Eo 8.85418782 × 10-12
in this case as there is a insulator occupying the area inbetween does that mean then their is no free space ??
Also in this equation the variable A is the area of...
Hello everyone,
I have calculated the received power for free space optic (FSO) using the equation:
Lsystem (system loss) is set to 8dB. PTotal can be calculated as:
where Ntx (number of receiver) = 1 and PTx (transmitted power) =7.78 dBm. LGeo can be calculated as:
where d2R (receiver...
The permittivity of free space, ε0, is usually given without any derivation or historical context as to how it was experimentally determined.
Could you explain to me how the value of ε0 was first determined experimentally or provide a resource that gives such a derivation?
Thanks!
as we know light travel in vacuum because of oscillation of electric and magnetic field and both are perpendicular to each other. But i don understand how these electric and magnetic fields get generated in vacuum. as electric filed can vary by oscillating charge and that generate varying...
Hi everyone,
I'm reading about the solution of the wave equation in free space on Stratton - Electromagnetic Theory and Snider - PDE and I got a little confused. The wave equation in 3D (plus time) is the following $$\frac{\partial^{2} \Psi (x,y,z,t)} {\partial t^{2}}=\nabla ^{2}\Psi...
Homework Statement
[/B]
A rope with uniform mass distribution is attached to a spaceship. At the end of this rope, there is a mass, m. The length of the rope - l.
Point A - where the rope is attached to a spaceship
Point B - in the middle of the rope.
The whole system moves with the same...
I have a doubt about coulomb's force equation in free space..ie 1/4πε0... Actually coulomb found that force exerted b/w charges are directly proportional to the product of charges and inversely proportional to the sqr of the distance bw them.we can measure force exerted and distance of...
I know that path loss is proportional to the square of the distance between the transmitter and receiver AND is also proportional to the square of the frequency in use but what does it mean when a free space calculator shows a negative number? How is it possible to get zero loss? For instance...
Permeability is the measure of the ability of a material to support the formation of a magnetic field within itself. And the inductance of an electric circuit is one henry (H) when an electric current that is changing at one ampere per second results in an electromotive force of one volt across...
In free space there are two masses:
- Metallic sphere of mass M, radius R and total charge equal to 0. It has also a resistivityρ.
- Metallic sphere of mass m, radius r and charge q.
The distance between the masses is D. We can assume r <<R<<D and m<<M. The masses start accelerating until they...
Homework Statement
In a lab that I did in Physics we calculated the magnetic field of a solenoid while constantly increasing the number of time the wire was wrapped around the electromagnet. After I obtained all the values, plotted it in a graph and found the line of best fit, the slope came...
Hi All,
what is the reason why very close to an electromagnetic source (Fresnel Region), the wave impedance Z0 in free space for electric field and magnetic field is not the same? Z0 for magnetic field increases and for electric field decreases by increasing the distance from the source...
Hello,
A quantum free particle (no forces acting on it) is usually introduced as a plane wave. A plane wave has a very specific momentum and energy but the function is not normalizable and the particle has a change to be everywhere in space. Mathematically, this plane wave cannot be...
Homework Statement
Two waves of different wavelengths λ1= 1.5μm, λ2 = 1.63μm, are combined in free space Et = 1.5cos(k1x - ω1t) + 2cos(k2x -ω2t)
Find the beat frequency
Homework Equations
(ω1- ω2) = 2ωm=beat frequency
E02 = 4E012cos2(kmx - ωmt)
The Attempt at a Solution
I am quite stuck on...
Homework Statement
How many orders of magnitude smaller is the average drift velocity of a hole than the RMS thermal velocity of an electron moving in free space? (Use the law of equipartition to find the RMS thermal velocity of a free electron.)
This is the last part of the problem, I have...
For a plane wave traveling in free space we know from Maxwell's equations that:
Z= E/H=√μ0/ε0 = 377Ω
The meaning of the wave impedance is that if we have an electric field oscillating with amplitude E0 in a medium (in this case the vacuum) a magnetic field will be induced with amplitude E0/Z...
Hi all,
I am interested in finding the power of a laser diode as function of the distance z, assuming a free space propagation. I think to have enough information to work it out but I am stacked at the moment.
Given:
the initial power, P0 = 1mW
beam width clip (e-2 = 13.5%), wx = 3μm, wy =...
Homework Statement An ideal solenoid is expected to generate a dipole field that falls off quickly as you move away from the solenoid. The magnetic field at distance r along the axis of the solenoid is given by B = (Mo/ 2pie) (M/r^3) In this equation the parameter M is called the dipole moment...
What actually is permittivity of free space I know it is εo and I know it's value but I want to know it's physical meaning,what does it actually do ?I have referred this
https://www.physicsforums.com/threads/what-is-permittivity.763156/#post-4804922
but did not get the answer.
I have also...
Is it possible to create a space void of photons? Or rather free from photon interference? I know single photon emitters have been made to test the behaviour of photons. However it would appear that space...well everything is jam packed with photons in various forms, and therefore "observing" a...
I am trying to understand the proof for Earnshaw's theorem. Though the theorem states
> that a collection of point charges cannot be maintained in a stable stationary equilibrium configuration solely by the electrostatic interaction of the charges ([Wikipedia][1])
In the proof, Gauss's Law in...
BBC has a small article on how Prof Daniele Faccio of Heriot-Watt University and Prof Miles Padgett of Glasgow slowed a photon to less than c in "free space", which I pressume to mean a vacuum.
Done by "changing the photon's shape" via some medium. When the photon returned to "free space" it...
My textbooks says in a region where there is no charge or current Maxwell's equations read
divergence of E=0
Curl of E=-dB/dt all d are partial
Divergence of B=0
Curl of B=ue(dE/dt)
I get the math of showing that there are waves, but I don't get some of these conditions. 1st don't you...
Hello.
I'm having trouble with determining the dynamics of a rod, when one of the ends has a torque applied to it. I've illustrated it in the figure below:
There are no external forces except of the torque - so no gravity, drag etc. Also, the rod is assumed rigid. How will it behave...
Hey everyone,
A meager pea brain (me) is in need of some help from you fine physics gentlemen.
This is a concept I've spend a lot of time pondering on (more than I would like to admit).
Imagine a rod of uniform density in free space. If you apply impulse onto the center of mass then it...
When we talk about the permeability of free space, are we talking about something with physical meaning on its own? Or is it simply a useful constant?
If it does have meaning on its own, what exactly is that meaning?
It is true that under ELECTROSTATIC CONDITIONS, excess charge on a conductor always resides on the surface of the conductor because if they were inside it, there would be an electric field inside the conductor which would set the free electrons into motion. They distribute uniformly over the...
Hi, could anyone help me understand the permittivity of free space in Gauss's Law:
\Phi = q/\epsilon0
If you consider a point charge in a box then I think it tells you how easy it is to establish an electric field in free space. But what happens if the medium is not free space - say you...
Homework Statement
(i) What is the phase velocity of EM radiation in free space?
(ii) What is its group velocity?
Homework Equations
The Attempt at a Solution
Using the definition as per this page:
http://physicsdaily.com/physics/Phase_velocity
(i) Vp = (C^2)/Vg
(ii)...
Good morning,
in circuit theory I know that reacting power arise from phasors and represents a power which can't be used, because not delivered to any load, but continuously flows back and forth between the load and the generator with a zero mean during one period.
I can't understand very well...
Homework Statement
Determine if the following diagrams may describe an electrostatic field in a charge-free space. The rectangles are the spaces under consideration. In the first four diagrams there are field lines while in the last two there are equipotential lines
Homework Equations...
If we take the perspective that free space is permeated with a sea of virtual particles, popping in and out of existence, it seems reasonable that such a sea would experience some amount of electric polarization in the presence of an electric field. That is to say, positively charged virtual...
Hello physicsForum..
I am trying to make a 2d physics engine for my game all on my own but I am stuck in the very basic problem. My problem is this..
If there is a rectangular body (with negligible depth since i am working on 2d) is present in free space as in attached file and a force of...
Homework Statement
A Hertzian dipole at origin generates a signal in empty space which is detected at a wire loop with position vector;
r=(50m)ez
Homework Equations
Signal is detected by changing magnetic field;
B(t)=B0 sin(2∏ft)ex
Show it is consistent with the Maxwell's solution to a plane...
μμHomework Statement
Permeability of free space:
symbol: μ
value: 4∏x10-7
Homework Equations
How would this be input to a calculator?
(4∏)x10-7
4x ∏x10-7
The Attempt at a Solution
so the actual number is 1.2566x10-6 is it?
Why is there no equation for solving for the magnetic field produced by multiple charges in free space? To solve for this do you sum up all the magnetic fields produced by each of the point charges or what?
Can electric field lines intersect in free space?
I found the answer on the internet, but I will like to understand why not?
Graphics will be appreciate it a lot!
Thanks
how does this change with introduction of another charge in its vicinity suddenly..and how does this vary as both charges repel each other after introduction of like charge..
btw I even wonder whether a electron which is outside a atom is in form of wave or particle..hope my questions are...
See attachment for my text's explanation's on the permittivity and permeability of free space, if you want but it's not necessary. Anyway, after reading those explanations of the p & p of free space I'm having a very difficult time understanding why taking the inverse square root of the product...
Homework Statement
Determine whether set is a vector space. If not, give at least one axiom that is not satisfied.
the set of vectors <a1,a2>, addition and scalar multiplication defined by:
<a1,a2>+<b1,b2>=<a1+b1+1,a2+b2+1>
k<a1,a2>=<ka1+k-1,ka2+k-1>
The Attempt at a Solution
For...