29. || A 2.0-cm-diameter parallel-plate capacitor with a spacing of 0.50 mm is c

Question

29. || A 2.0-cm-diameter parallel-plate capacitor with a spacing of 0.50 mm is charged to 200 V. What are (a) the total energy stored in the electric field and (b) the energy density? Section 29.7 Dielectrics 30. || Two 4.0 cm x 4.0 cm metal plates are separated by a 0.20-mm-thick piece of Teflon. a. What is the capacitance? b. What is the maximum potential difference between the plates? 31. || Two 5.0 mm X 5.0 mm electrodes with a 0.10-mm-thic sheet of Mylar between them are attached to a 9.0 V batter Without disconnecting the battery, the Mylar is withdraw (Very small spacers keep the electrode separation unchange What are the charge, potential difference, and electric f (a) before and (b) after the Mylar is withdrawn?

Explanation / Answer

Area = 0.04m*0.04m = 0.0016m^2
distance = 0.2mm = 2*10^-4 m

Dielectric constant of Teflon (k) = 2.1

dielectric strength Emaximum= 6.0 x 10^7 V/m
a
C = k*Eo*A / d
    = 2.1*8.854*10^-12*0.0016 / 2*10^-4 F = 1.49*10^-10 F
    = 0.149 nF

b.
EMaximum = 6.0*10^7 V/m (Volts per m, not V = m)

Voltage maximum = EMaximum * d = 6.0*10^7 V/m * 2*10^-4m = 12000 V
Voltage maximum = 12 kV

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