A.) True FalsAfter being disconnected from the battery, inserting a dielectric w

Question

A.) True FalsAfter being disconnected from the battery, inserting a dielectric with ? will increase C.
True False After being disconnected from the battery, inserting a dielectric with ? will increase U.
True False After being disconnected from the battery, decreasing d increases U.
True False With the capacitor connected to the battery, decreasing d decreases Q.
True False After being disconnected from the battery, decreasing d increases C.
True False After being disconnected from the battery, inserting a dielectric with ? will decrease V.

B.)A parallel-plate capacitor made of circular plates of radius 25 cm separated by 0.35 cm is charged to a potential difference of 1000 volts by a battery. Then a sheet of mylar 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 mylar 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

Explanation / Answer

After being disconnected from the battery, inserting a dielectric with ? will increase C.
true
After being disconnected from the battery, inserting a dielectric with ? will increase U.
False
After being disconnected from the battery, decreasing d increases U.
true
With the capacitor connected to the battery, decreasing d decreases Q.
false
After being disconnected from the battery, decreasing d increases C.
false
After being disconnected from the battery, inserting a dielectric with ? will decrease V.
true

b) find the capactance.
C = (0 * A)/d = (8.85e-12 * * 0.252 ) / (0.35e-2) = 4.965e-10 F

find the charge when no dielectric material is inserted.

Q = CV = 4.965e-10 * 1000 = 4.965e-7 C

when dielectric material is inserted.

kQ = 3.1 * 4.965e-7 C = 1.539e-6 C

the difference between the charges

1.539e-6 - 4.965e-7 = 1.0425e-6 C

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