A parallel-plate capacitor made of circular plates of radius 25 cm separated by

Question

A parallel-plate capacitor made of circular plates of radius 25 cm separated by 0.25 cm is charged to a potential difference of 1000 volts by a battery. Then a sheet of polyethylene is pushed between the plates, completely filling the gap between them. How much additional charge flows from the battery to one of the plates when the polyethylene is inserted?

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Dielectric constant for some materials:
mylar 3.1
polyethylene 2.6
polyvinyldifluoride 11.
tantalum pentoxide 25.
Teflon 2.1

Please show all work! I will rate very well! Thanks!

Explanation / Answer

First calculate the capacitance Co of the empty capacitor from its area A=pir^2 and plate separation d using the parallel plate capacitor formula; Co = eoA/d Then use that to calculate the initial plate charge Qo from the given voltage V as; Qo = CoV When the dielectric, of constant K=11 , is inserted the new capacitance is C=KCo and the new charge Q is found from (since the voltage is the same); Q = CV = KCoV = KQo So the amt. of additional charge added by the battery is; dQ = Q - Qo = (K-1)Qo = 10Qo So find Qo from the first and second formulas, then multiply by 10 and you're done.

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