Physics 212 lecture 9: Dielectrics

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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

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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?

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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..
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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