A parallel plate capacitor (air filled) that is maintained at a 20.0 V potential

Question

A parallel plate capacitor (air filled) that is maintained at a 20.0 V potential difference between plates.  It has a plate area of 7.60 cm2 and a plate separation of 1.80 mm.  Calculate the electric field between the plates, the surface charge density, the capacitance, and the charge on each plate.

A parallel plate capacitor (air filled) that is maintained at a 20.0 V potential difference between plates. It has a plate area of 7.60 cm2 and a plate separation of 1.80 mm. Calculate the electric field between the plates, the surface charge density, the capacitance, and the charge on each plate.

Explanation / Answer

So l u t i o n :

(a)

E =V/d

=20.0 V/1.80" 10-3 m

= 1.11" 104 V m

=11.1 kV m directed toward the negative plate

(b)

C =

e0*A/d

=8.85 " 10^-12 C2 Ncm2 ( )7.60" 10^-4 m2 ( )/1.80 "10-3 m

= 3.74 *10^-12 F = 3.74 pF

(c)

Q = C(V) = 3.74" 10^-12 ( F)(20.0 V) = 7.47 "10^-11 C = 74.7 pC on one plate and

-74.7 pC on the

other plate.

surface charge density = 2Q*e0

= 2*74.7*10^-12* 8.85*10^-12

= 1322.19 C/m^2

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