A parallel plate capacitor with plate separation d is connected to a battery. Th

Question

A parallel plate capacitor with plate separation d is connected to a battery. The capacitor is fully charged to Q Coulombs and a voltage of V. (C is the capacitance and U is the stored energy.) Answer the following questions regarding the capacitor charged by a battery. For each statement below, select True or False.

After being disconnected from the battery, inserting a dielectric with %u03BA will decrease U.
After being disconnected from the battery, decreasing d increases U.
After being disconnected from the battery, inserting a dielectric with %u03BA will decrease V.
After being disconnected from the battery, increasing d increases V.
With the capacitor connected to the battery, inserting a dielectric with %u03BA will decrease C.
With the capacitor connected to the battery, increasing d increases C.

Explanation / Answer

When the battey is disconnected the charge on the capacitor plates wont change.

a)True. Since the energy stored in the capacitor is Q^2/(2C) and C is directly proportional to dielectric constant.

b) False Since the energy stored in the capacitor is Q^2/(2C) and C is inversely proportional to 'd'.

c) True, voltage will decrease Q=CV as charge is same, and capacitance increases voltage will reduce.

d) True, voltage will increase Q=CV as charge is same, and capacitance reduces voltage will increase.

e) False (C increases)

f) False (C decreases)

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