1 / 14

Fields and Waves

Fields and Waves. Lesson 3.4. ELECTROSTATICS - MATERIALS. CONDUCTORS and DIELECTRICS. Conductors. Dielectrics. High conductivities; s (for Copper) ~ 5.8x10 7 S/m. Low conductivities; s (for Rubber) ~ 1x10 -15 S/m or 1/ W -m. Semiconductors (mid s ’s).

Télécharger la présentation

Fields and Waves

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.


Presentation Transcript

  1. Fields and Waves Lesson 3.4 ELECTROSTATICS - MATERIALS Darryl Michael/GE CRD

  2. CONDUCTORS and DIELECTRICS Conductors Dielectrics High conductivities; s (for Copper) ~ 5.8x107 S/m Low conductivities; s (for Rubber) ~ 1x10-15 S/m or 1/W-m Semiconductors (mid s’s) Permittivities, e = 1-100e0 Note: e0 is the permittivity of free space/vacuum = 8.854 x 10-12 F/m

  3. CONDUCTORS Most electrons are stuck to the nucleus But, 1 or 2 electrons per atom are free to move This means that if you apply an external E-field, the free electrons will move Lattice of Nuclei

  4. - - + + + + - - - - + + - - + + - - + + CONDUCTORS conductor electrons Apply external E-field, • Force on electrons causes free electrons to move • Charge displacement causes response E-field (opposite to applied external E-field)

  5. , in a conductor Conductor is equipotential CONDUCTORS The electrons keep moving until, This means that: Do problem 1

  6. + + DIELECTRICS electron cloud nucleus electron cloud centered on nucleus Cloud shifts to setup

  7. Define: dipole moment Polarization partially cancels applied Field DIELECTRICS

  8. DIELECTRICS subtracts out bound charge Define: Displacement Flux Density ( C/m2 ) Electric Field (V/m) is due to bound/dielectric charge and free charge is due to bound/dielectric charge only and opposite sign is due to free charge only

  9. FREE CHARGES Examples of free charges: rs on conductor electron beam doped region of semi-conductor Gauss’ Law uses just free charge Most general form

  10. Don’t need to know about bound charges to find Many materials have Define , where Typically, DIELECTRICS Do Problem 2

  11. Damages materials - there is a Voltage limit on components, cables in air : = 30 kV/cm DIELECTRIC BREAKDOWN - part d of problem Example: Arc in Air If E-field is too large, it will pull electrons off from atom These electrons are accelerated by the E-field These accelerated electrons then collide with more atoms that knock off more electrons This is an AVALANCHE PROCESS BREAKDOWN OCCURS if

  12. BOUNDARY CONDITIONS - Normal Components • all derived from Maxwell’s equations NORMAL COMPONENT Take h << a (a thin disc) a Material 1 TOP h Material 2 BOTTOM Gaussian Surface

  13. BOUNDARY CONDITIONS - Normal Components REGION 2 is a CONDUCTOR, D2 = E2 =0 Case 1: Case 2: REGIONS 1 & 2 are DIELECTRICS with rs = 0 Can only really get rs with conductors

  14. BOUNDARY CONDITIONS - Tangential Components w Material 1 h << w h Material 2 If region 2 is a conductor E1t = 0 Note: Outside conductor E and D are normal to the surface

More Related