The voltage across an air-filled parallel-plate capacitor is measured to be 237.

Question

The voltage across an air-filled parallel-plate capacitor is measured to be 237.0 V. When a dielectric is inserted and completely fills the space between the plates as in the figure below, the voltage drops to 69.7 V.

(a) What is the dielectric constant of the inserted material?


Can you identify the dielectric?
---Select--- bakelite /neoprene rubber/ paper/ nylon/ teflon

(b) If the dielectric doesn't completely fill the space between the plates, what could you conclude about the voltage across the plates?

Explanation / Answer

dielectric constant by using the formula:

C = kC' (where C is the capacitance and k is the constant)

and then noting that C = Q/V (Q=charge, V=voltage)

We know that charge is constant, and that only the voltage changes, hence we can rewrite the first equation as:

V1*C = V2*k*C

Simplifying and solving for k we get:

k = V1 / V2 = 237 V / 69.7 V    =     3.4
k = 3.4


Part B,

a k value of 3.4 would be nylon

(*other k values are as follows:    nylon = 3.4, paper = 3.7, neoprene rubber = 6.7, teflon = 2.1)

Part C,

Since the dielectric doesn't completely fill the space, that means the voltage is not at the minimal point it could be at.

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