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Flashcards in Dieletrics Deck (9)
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1
Q

How can charge stored between plates be increased?

A
  • inserting a dielectric between the plates
  • dielectrics are electrically insulating materials that increase the ability of a parallel-plate capacitor to store charge when dielectric is placed between the plates of the capacitor
  • polythene and waxed papers are examples
2
Q

What happens when a dielectric is placed between the oppositely charged parallel plates connected to a battery?

A
  • becomes polarised
    • electrons are pulled slightly towards the positive plate
    • surface facing the +ve plate gains a -ve charge
    • vice versa
    • each molc has its own electrc field, which in the alignemnts opposes the applied magnetic field
  • more charged stored on the plates because
    • the positive side of the dielectric attracts more electrons from the battery onto the -ve plates
    • the -ve side of the dielectric pushed electrons back to the battery from the +ve plates
3
Q

What is relative permittivity?

A
  • εr
  • aka dielectric constant
  • ratio of charge stored w/ the dielectric to the charge stored without the dielectric is defined as the relative permittivity of the substance
  • εr = Q / Q0
    • Q = charged stored by parallel-plates when space completely filled with dielectric
    • Q0 = empty
  • also = C / C0
4
Q

Water has a large relative permetivitty constant, what does this explain about waters oproperties?

A

explains why salts can dissolve in water

5
Q

What is the equation for capacitance when filled with dielectric?

A
  • C = Aε0εr / d
    • A is surface area of each plate
    • d is spacing
6
Q

What does this equation show how to make a large capacitance?

A
  • increasing area
  • decrease plate spacing
  • filling the space between plates w/ dielectric with a larger relative permeativityy
7
Q

What happens in an alternating electric field?

A
  • polar dipolses roate
  • non-polar dipolses oscillate alternating ways and the field strength increases and decreases
8
Q

What is permittivity

A

measure of how difficult it is to generate an electric field in an equaitom

9
Q

Explain why there is an increase in the energy stored by the capacitor when the polythene sheet is pulled out from between the plates.

A
  • Energy increases
  • In the polar dielectric molecules align in the field with positive charged end toward the negative plate
  • Work is done on the capacitor separating the positively charged surface of the dielectric from the negatively charged plate