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-Capacitors with Dielectrics -Types of Capacitors

-Capacitors with Dielectrics -Types of Capacitors . AP Physics C Mrs. Coyle. Dielectric:. A nonconducting material that, when placed between the plates of a capacitor, increases the capacitance Dielectrics include rubber, plastic, and waxed paper

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-Capacitors with Dielectrics -Types of Capacitors

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  1. -Capacitors with Dielectrics-Types of Capacitors AP Physics C Mrs. Coyle

  2. Dielectric: • A nonconducting material that, when placed between the plates of a capacitor, increases the capacitance • Dielectrics include rubber, plastic, and waxed paper • If the dielectric completely fills the space between the plates, the capacitance increases by a factor κcalled the dielectric constant. C= κ Co

  3. Effect of Dielectric on Voltage across a Capacitor • Potential difference across the plates with a dielectric is less than the potential difference • across free space • Does the C change with or without the dielectric?

  4. If the V is kept constant by a battery and then a dielectric slab is inserted between the plates, the charge between the plates increases by a factor of κ.

  5. Effect of a Dielectric on E, C • Eo, Co are the values without a dielectric (free space or air between plates) • Electric field between the plates is weaker with dielectric • Capacitance is greater with a dielectric • More charge is stored in the capacitor

  6. Example of Dielectric Constants for Various Materials “Dielectric strength” : maximum field in the dielectric before spark discharge

  7. Dielectrics • In theory, d could be made very small to create a very large capacitance • In practice, there is a limit to d • d is limited by the electric discharge that could occur though the dielectric medium separating the plates • For a given d, the maximum voltage that can be applied to a capacitor without causing a discharge depends on the dielectric strength of the material

  8. Dielectrics, final • Dielectrics provide the following advantages: • Increase in capacitance • Increase the maximum operating voltage • Possible mechanical support between the plates • This allows the plates to be close together without touching • This decreases d and increases C

  9. Tubular Capacitors • Metallic foil - thin sheets of paper or Mylar, layers are rolled into a cylinder

  10. Electrolytic Capacitors • Used to store large amounts of charge at relatively low voltages • The electrolyte is a solution that conducts electricity by virtue of motion of ions contained in the solution

  11. Variable Capacitors • Variable capacitors consist of two interwoven sets of metallic plates • One plate is fixed and the other is movable • These capacitors generally vary between 10 and 500 pF • Used in radio tuning circuits

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