An air filled parallel-plate capacitor is charged by connecting
it to a battery.
The battery is then disconnected from the capacitor without any
loss of
charges. (a) A voltmeter reads 60 V across the plates. When a
dielectric is
inserted between the plates, completely filling the space, the
voltmeter reads
12.5 V. What is the dielectric constant of the dielectric material?
(b) What will
the voltmeter reading be if the dielectric is now pulled partway
out so it fills only
one-third of the space between the plates?