The voltage across an air-filled parallel-plate capacitor is measured to be 110.
ID: 1376087 • Letter: T
Question
The voltage across an air-filled parallel-plate capacitor is measured to be 110.0 V. When a dielectric is inserted and completely fills the space between the plates as in the figure below, the voltage drops to 32.4 V.
(a) What is the dielectric constant of the inserted material?
(b) Can you identify the dielectric?
nylon
paper
bakelite
neoprene
rubber
teflon
(c) If the dielectric doesn't completely fill the space between the plates, what could you conclude about the voltage across the plates?
Explanation / Answer
Capacitance of parllel plate capacitor without inserting the dilectric medium, C0 is given by:
C0 = Eo A / d ( E0 = permitivity of free space ie air, A = area of plates, d = distance between plates0
Q0 / V0 = E0 A / d -----------------1 ( from Q = CV , C = Q/V)
Capacitance when dilectric is inserted:
C = E A / d ( E = permitivity of medium , also E = E0 *K
Q/V = E0 *K *A/ d ---------------2 ( K = dilectric constant )
By dividing eq 2 by 1
V0 / V = K
K = 110/ 32.4 = 3.39
( B ) If we compare K = 3.39 with minimum value of dilectric constant for nylon which is 3.4, then
According to this material should br nylon.
( C ) When the dielectric constant completely filled the space, then capacitance become maximum so voltage minimum.
But When dilectric doesn't fill the space then capacitance will have value between least and maximum value of capacitance.
From C = Q / V , then voltage will have value between least and maximum value of voltage.
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