# What is Flux: Definition and 1000 Discussions

Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. A flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport phenomena, flux is a vector quantity, describing the magnitude and direction of the flow of a substance or property. In vector calculus flux is a scalar quantity, defined as the surface integral of the perpendicular component of a vector field over a surface.

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1. ### Calculating the flux of a vector field

I am not sure why latex is not rendering, but here is the question. The answer is ##\frac{a^2}{8}## and for the love of my life, I don't know how. Can you please help me with this?
2. ### Gamma Ray Shielding -- How much is enough?

If Shielding is required for gamma ray flux of 1e23 (let say E=1 Mev). As Shielding cannot fully attenuate flux to zero, how much percentage is technically recommended for shielding of above flux?. So far as I know shield thickness is considered to minimise dose/flux Upto 1/10 of its...
3. ### I Magnetic Flux - Misleading Definition or what?

Magnetic flux density(B) is defined as, magnetic force per unit pole strength and flux is defined as magnetic field passing normally through given surface. I think, I am clear about these definitions, and quantitative meaning they carry. I usually find, in some texts, the definitions as in image...
4. ### Run MCNP 5 input file of certain geometry for flux calculation

Can any one please explain if I want to run mcnp 5 input file of certain geometry for flux calculation on different surfaces. So far as I know If I increase the NPS (number of particles) it wll give more accurate result but when I increase NPS from 10e9, input file do not run and close within a...
5. ### Deriving the kinetic energy flux in an effusion process

I could not find any derivations in the litterature, except for the expected value of the energy flux expression itself: $$\overline{\Phi_{effusion,\epsilon}} = \overline{\dot{N_{ef}}}\overline{\epsilon_{ef}}=\frac{3Nl}{2A}\sqrt{\frac{(k_BT)^3}{2\pi m}}$$ I've started off by calculating the...
6. ### Flyback Converter Magnetic Flux Calculation

Hi I am designing a flyback converter. The calculation (.jpg file) is based on Daniel W. Hart Power Electronics book. The transformer model consists only of an ideal transformer and its magnetizing inductance (or "primary inductance" in some textbooks). The datasheet of the transformer's core...
7. ### Electric Flux through a semi-spherical bowl from a charged particle

I believe this does has a couple of Calculus aspects to it but I don't really know how I'd find the surface area of inside the bowl. The answer sheet says the answer is 252 with a margin of error of +/- 1
8. ### I Some reasoning about Alfvén’s frozen-in flux theorem

Alfvén’s theorem is very famous in plasma physics. It is also often used in astrophysics. The link in Wiki: https://en.wikipedia.org/wiki/Alfv%C3%A9n%27s_theorem However, after a series of continuous reasoning, it seems that this theorem has problem. What errors can be hidden in the reasoning...
9. ### Relationship between magnetic field lines and magnetic field

As stated in the problem, I want to demonstrate mathematically that field line density is directly related to the magnitude of B. How would I be able to do this, other than simply using the flux equation and showing that for a higher flux in the same area, the magnetic field must be rise...
10. ### Flux from magnet (Why is the Flux not zero through the loop?)

For the problem attached, Why is the magnetic Flux not zero through the loop? Many thanks!
11. ### The direction of flux vectors in derivation of conservation of mass

In the derivation of the conservation law of the conservation of mass, the flux on one side enters and the flux on the other side leaves the control volume. I presume this is due to the assumption that the volume is infinitesimally small and hence v(x,y,z,t) will not change directions...
12. ### Alternative method of finding Electric flux from non-uniform field

For this problem, The solution is, However, why can the differential area not be: I tried integrating and got, Can someone please tell me what I have done wrong? Thank you!
13. ### Flux through top part of sphere

Flux=$$\iint(xz, -yz, y^2)\cdot(x,y,z)/\sqrt{2} dA=\int_0^{2\pi}\int_0^1 r^2\cos^2\theta \sqrt{1-r^2/2} rdrd\theta$$. Integrating this doesn't give the correct answer of ##\pi/4##.
14. ### Flux density help please (seawater flowing in a tube)

What is the flux density of salt in a horizontal tube 10 cm in length connecting seawater (salinity = 30 g/l) to a tank of freshwater (salinity ~ 0) assuming no advection occurs?
15. ### I Incorrect units when calculating cosmic ray muon flux

I recently performed an experiment that involved using a cylindrical scintillator to detect cosmic ray muons by observing the amount of particles that decayed within 20 microseconds over a long period of time. I'd like to use this to find the flux of muons at my scintillator so that I can...
16. ### Magnetic flux with magnetic field changing direction

Sorry if I post again about this topic (last time I promise!) but I still have some doubts regarding the concept of flux. This collection of problems I have quite standard but there are so many variations. Here is the circuit in question: Something tells me that I could write a function that...
17. ### Magnetic flux of magnetic field changing as a function of time

$$B(t) = B_{0} \frac{t^2}{T^2}$$ for ##0 \leq t \leq T## The issue here is more conceptual, because once I find the flux of B I know how to proceed to find the current. I got velocity (but it seems to me that it is the initial velocity), I could use it to find the time in function of space...
18. ### I Interpreting solar event flux units

Hi, I wanted to find the number of protons striking a surface area during a solar event and the units provided are: #/(cm^2 s sr). Say I have a 1 m^2 surface area directly facing the sun, how do I use those units to discover the number of protons/s. What is the value of the solid angle to...
19. ### Engineering Calculating maximum flux density

Hi everyone, I have a EE problem that I need to sort out for alternating voltage. I have to find out the maximum flux density. B_max= integral from 150 degrees to 30 degrees (u/(2NA) dt is my problem. I have a hard time to integrate this since I am to integrate with time and not degrees or...
20. ### Find surface of maximum flux given the vector field's potential

The vectorfield is $$A = grad \Phi$$ $$A = x^2 + y^2 + z^2 - (x^4 + y^4 + z^4 + 2x^2y^2 + 2x^2z^2 + 2y^2z^2)$$ The surface with maximum flux is the same as the volume of maximum divergence, thus: $$div A = 6 - 20(x^2 + y^2 + z^2)$$ This would suggest at the point 0,0,0 the flux is at maximum...
21. ### A Probability flux integrated over all space is mean momentum?

In Sakurai Modern Quantum Mechanics, I came across a statement which says probabiliy flux integrated over all space is just the mean momentum (eq 2.192 below). I was wondering if anybody can help me explain how this is obtained. I can see that ##i\hbar\nabla## is taken as the ##\mathbf{p}##...
22. ### Leakage Flux Inside a Slot of an AC Machine (dual stator)

Hello All, Please see the attachments. The pdf file is the IEEE paper I'm reading. Figure 1 show a slot of the AC machine similar to the front view of the picture below: But in one slot, they fit two sets of conductors. The first set carries current i1 in total. The second set carries...
23. ### MCNP Flux and Power Calculation

During a reactor assembly calculation, I need to determine axial and radial flux distribution over the surface. When I use F2 and F4 tally I get some value with unit 1/cm**2 What does the value means, neutron flux is supposed to be in the 10^14 range but output values are 10^2 range. Can anyone...
24. ### Flux of Electric field through sphere

My attempt: We have 3 charges inside 2 +ve and 1 -ve so i just added them up. 4 + 5 +(-7) = 2q Then there is a -5q charge outside the sphere. I did 2q + (-5q)= -3q . The electric field flux formula is Flux= q/ E0 . So i got -3q/E0 which is obviously wrong : ) . After quick googling , I...
25. ### Too Much Stellar Flux: Fixing a 25-year old Problem

Short version: problems fixing 25-year old world-building; due to canonised data points, I have a planet that is way too hot to work, compounded by interpretation problems by teenage-me on stellar data - help would be appreciated! Sometime in around the mid 1990s, I got SpaceMaster the RPG...
26. ### I Derivation of the magnetic flux in coaxial cable

The magnetic flux ##\phi_m = \int{BdA}## The magnetic field of the coaxial cable B = ##\frac{I_{enc} \mu_0}{2\pi r}## since surface area of a cylinder = ##2\pi rdr L, dA = 2\pi L dr## where L is the length of the coaxial cable so ##\phi_m = \int{\frac{I_{enc} \mu_0}{2\pi r}2\pi L dr}##?
27. ### COMSOL simulation of a 3D Ferrite Bar Numerical Model For Magnetic Flux

Hi, I am willing to simulate a 3D ferrite bar transmitter and reciever where coupling coefficient k and Bt magnetic flux density on the each side uses the finite element method for solving partial differential equations. The Magnetic Fields module has equation (jωσ − ω2ε0εr)A + ∇ × H = Je...
28. ### Flux of constant magnetic field through lateral surface of cylinder

If the question had been asking about the flux through the whole surface of the cylinder I would have said that the flux is 0, but since it is asking only about the lateral surfaces I am wondering how one could calculate such a flux not knowing how the cylinder is oriented in space. One could...
29. ### What is wrong with this flux integral?

I think the issue is how I parameterize my vector field, but not quite sure. In case you were wondering, this is problem # 27, chapter 16.7 of the 8th edition of Stewart. Thanks for any help.
30. ### I Electric field, flux, and conductor questions

1) Why is the electric field 0 at the bottom of Gaussian surface? Isn't the electric field on both sides of the surface, pointing down and outwards like a plane of charge? see image. 2) Why does a charge distribution with cylindrical symmetry have to be infinitely long? 3) My book says a...
31. ### I Calculation of electric flux on trapezoidal surface

I am confused at this calculation of the electric flux through a trapezoidal surface. The flux in should equal the flux out. The flux in equals -E*A1 where A1 is the area of the bottom of the trapezoid. The flux out equals E*A2 where A2 is the area of the top of the trapezoid. But the two fluxes...
32. ### I Question regarding the use of Electric flux and Field Lines

1)Field Lines is supposed to represent the electric field around a charge ,now we can draw infinite field lines around a charge and sinc Electric flux is No of Field Lines /area ,does it become infinite ,the whole concept of field lines is quite in the Gray Area for me ,I can in theory mark...
33. ### I Kappa factor in heat equation and heat Flux

I am doing a project, actually it is a simulation. And we aim to determine the spatial and heat flux evolution of the system. The system consists of two concentric cylinders separated by an insulating material. I change the value of kappa of the insulator but the heat flux remains always the...
34. ### I Energy flux direction in a conducting wire?

On the Internet, I have read that the energy doesn't flow in the wire, for example in a very simple electric circuit made of a battery and a closed loop. When one computes the Poynting vector ##\vec S \propto \vec E \times \vec B##, one gets that its direction is towards the center of the wire...
35. ### Flux of the electric field that crosses the faces of a cube

a) $$\phi_T=\phi_F-\phi_I=10^4\cdot 4\cdot 4-10^4\cdot 4\cdot 4=0\, \textrm{Nm}^2/\textrm{C}$$ b) $$\phi_F=\underbrace{300\cdot 4}_{\vec{E}}\cdot \underbrace{4\cdot 4}_{\textrm{area}}=19200\, \textrm{Nm}^2/\textrm{C}$$ $$\phi_0 = 300\cdot 0\cdot 4\cdot 4=0\, \textrm{Nm}^2/\textrm{C}$$ Then...
36. ### Toroidal Inductor Flux Calculation

Summary:: A 4.3 mH toroidal inductor has 100 identical equally spaced coils. If it carries an 11.6 A current, how much magnetic flux passes through each of its coils? Express your answers in milliwebers. 4.3 mH= (Wb/A) 100= N 11.6= I Φcoil= ? So from my observation of another question...
37. ### Electrical flux passing through the cube

Picture for better understanding. My answer : I want to know how to solve this problem without using cylindrical. I mean how can we solve this using cube and its sides. Thanks.
38. ### Find the flux of a vector field

Question: Equation: Attempt: Can someone verify my answer?

40. ### B Measuring Light's Brightness & Power Flux Relative to Observer's Speed

Assuming that the observer moves along the direction of the light, does the speed of the observer's measuring instrument relative to the light source (which may be close to the speed of light) affect the brightness and/or power flux density measured by the observer? I'm not sure about this...
41. ### B Electric flux density and confusion about units

My general understanding of electric flux density is 'electric flux per unit area'. This gives the SI unit N/C. But According the formula of electric flux density, D=eplison*E, the SI unit is C/m^2. How come the dimension in both cases not matching if both are true?
42. ### B Electric flux -- Which of these three definitions is correct?

I have read three definitions of electric flux in textbook which is confusing me.. 1. Electric flux is the number of electric lines passing through any area of a surface. 2. Electric flux is the number of electric lines passing through unit area per second held perpendicularly. 3. Electric flux...
43. ### Engineering Calculating the flux through a certain radius (concentric charged spheres)

Question My attempt for the 1st part, when r = 1.5 m Could someone confirm my answer?

45. ### Gauss' law and flux concept issues

Hi guys i have some concept issues about flux. My book says flux is proportional to the number of lines passing through that area. so my question is: first i am thinking that a 2D circle which has a 2r diameter and it is enclosing a 2q charge so its flux should be 2q/Epsilon.then i am thinking a...

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47. ### Electric Flux for a cube problem

I have tried to understand the solution given in the book which is as pasted below. The solution uses Gauss's Law but makes no mention of which Gaussian surface is used. The diagram that I have used to understand this problem is also given at the end. From the diagram, faces OADG, OABE and OEFG...
48. ### B Different formulas for electric flux

I noticed that in some textbooks (Physics - Tipler) the electric flux formula is different than in other textbooks (Engineering Electromagnetics -W. Hayt) Which one should we use?
49. ### Magnitude of the flux through a rectangle

I have attached the work to this problem and although it has different parameters than what I have listed in my post the basis to solving the problem is the same. I am confused on why this rectangle in this problem is considered to b in the j unit vector direction. Is it because its face will...
50. ### B Concept of flux

Phi= int(E.da) through a surface S is a measure of “number of field lines” passing through S. I put this in quotes because of course we can only draw a representative sample of field lines. The total number would be infinite. But for a given sampling rate the flux is proportional to the number...