The dielectric in a capacitor serves two purposes. It increases the capacitance,

Question

The dielectric in a capacitor serves two purposes. It increases the capacitance, compared to an otherwise identical capacitor with an air gap, and it increases the maximum potential difference the capacitor can support. Recall that air near the sphere of a Van de Graaff generator undergoes breakdown, creating a spark, when the electric field is sufficiently strong. The same is true for any material. That critical field strength, at which breakdown occurs, is 3.0 MV/m for air, but 60 MV/mfor Teflon.

Part A) A parallel plate capacitor consists of two 5.0cm

Explanation / Answer

PART A:

Note that

V = Ed

Here, for air,

E = 3.0 MV/m = 3E6 V/m
d = 0.50 mm = 0.00050 m

Thus,

V = 1.5E3 V

Now, as

U (energy) = CV^2/2

and

C = EoA/d

where

Eo = 8.85E-12 C^2/N m^2
A = (5.0 cm)^2 = 25 cm^2 = 0.0025 m^2
d = 0.000500 m

Then

U = EoAV^2/2d

U_air = 4.98E-5 J

**************************

In similar fashion.

U = EoAV^2/2d

V = Ed

Here, E = 60E6 V/m, thus,

V = 30000 V

Thus,

U_Teflon = 0.0199 J
******************************

DONE! It was nice working with you!

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