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Physics 212 lecture 9: Dielectrics

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regular commercial (metal foil strips separated by mylar) ... a capacitor made from rolls of aluminum foil, plastic wrap, and wax paper from the supermarket. ... – PowerPoint PPT presentation

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Title: Physics 212 lecture 9: Dielectrics


1
Physics 212 lecture 9 Dielectrics
  • The dielectric constant (?)
  • Different substances allow electric fields to
    pass through at different levels of
    effectiveness. A diminished electric field
    affects the voltage between two points.
  • Thus, the voltage between the plates of a
    capacitor may change with a different material
    between them even though the charge remains the
    same.
  • Some values (more on page 812)
  • ? 1 vacuum (empty space)
  • 1.00059 air
  • 2.5 silicone oil
  • ? 3.2 mylar
  • ? 80 water

2
Information about the construction of capacitors
  • regular commercial (metal foil strips separated
    by mylar)
  • high voltage (metal plates submerged in oil)
  • electrolytic (electrolye and metal foil separated
    by thin oxide layer)
  • Question why build them like this since vacuum
    or air have the best dielectric constant?

3
Example Ch 26 46Estimate the capacitance and
the breakdown voltage for a capacitor made from
rolls of aluminum foil, plastic wrap, and wax
paper from the supermarket..
4
Example Ch 26 48Titanium dioxide wafer has
?173, A1cm2, and thickness 0.1mm with Al metal
on faces and connected to a 12V battery. a) Find
C b) Find Q c) Find the surface charge density
d) Find E
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