Bar electret: when D is not εE
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- čas přidán 11. 12. 2023
- Using Maxwell's equations to work out the shape of the field lines of both E (electric field) and D (displacement field) produced by a bar electret with uniform polarisation. This is the electrical analog of a bar magnet!
About the displacement field: • What is the electric d...
Surface charge & polarisation: • Polarisation and surfa...
About me: I studied Physics at the University of Cambridge, then stayed on to get a PhD in Astronomy. During my PhD, I also spent four years teaching Physics undergraduates at the university. Now, I'm working as a private tutor, teaching Physics & Maths up to A Level standard.
My website: benyelverton.com/
#physics #mathematics #electromagnetism #electret #fieldlines #displacementfield #maxwellsequations #curl #divergence #displacement #vectorcalculus #irrotational #maxwellequations #boundcharge #freecharge #chargedensity #electriccharge #dielectric #electricfield #electricdipole #dipole #dipolemoment #dielectrics #insulator #materials #polarisation #polarization #vector #electrostatics #maths #math #science #education
Can't wait to see a series on the H field too!
Glad to hear it! That will probably be coming early next year.
Sir why haven't you uploaded in long time ?
Also can you make some videos on statistical mechanics from scratch as I trued to understand the Maxwell boltzmann distribution but couldn't find any good video with derivation :(
Just taking a short break over Christmas, I will be back soon! Will make sure to cover some statistical mechanics next year.
@@DrBenYelverton ok I will think of some suggestions by the time 😃
Sir I have a few unrelated questions
1) why do we assume that tension in a string is constant along the entire string
2) why is rotational kinetic energy 1/2Iw^2
1) Apply F = ma to an infinitesimal element of the string, and you get T₂ - T₁ = dm × a, where T₁ and T₂ are the tension forces pulling the element in two opposite directions. We often assume that dm = 0, which implies that T₂ = T₁, hence the tension is constant along the string. The result only holds if the string is either massless or not accelerating (or both), and assumes that no other forces (e.g. friction) act along the string. For an example of non-constant tension see my old video on the capstan equation: czcams.com/video/T4wVlOYFoH8/video.html
2) Summing the kinetic energies of all particles in a rigid body gives: Σ½mv² = Σ½m(rω)² = ½ × Σmr² × ω² = ½Iω², where the final step follows from the definition of I.
@@DrBenYelverton thank you sir 😀
@@DrBenYelverton sir I have an idea for video , you can make a video on solving JEE advanced or mains problem using different ways (like using lagrangian and Newtonian both) this would get a lot of views too as JEE is pretty popular amongst Indian students :)
And the problems are also great for solving. (But they are usually numericals so you could also try to generalize the solution)
A few people have suggested this, I will have to take a look at some of the papers some time!
What are the uses of the D field?
It shows up in the Maxwell equation and is a convenient way to describle electric field within matter. See the latest 4 videos for more explanation
Well, arguably finding the E field is the ultimate goal; it's more fundamental in the sense that E is what determines the force on a charged particle (via F = qE). The D field is not actually necessary at all, and Maxwell's equations are complete even if written only in terms of E. Taking this viewpoint, D is just a quantity that's introduced to make it easier to find E when there are dielectric materials involved. As @mingmiao364 mentioned, I have a couple of other recent videos explaining why exactly D can be sometimes be more convenient to work with.
@@DrBenYelverton ah ok thanks, I will check those out