An air-filled parallel plate capacitor is made from two thin sheets of aluminum

Question

An air-filled parallel plate capacitor is made from two thin sheets of aluminum foil, each of which is a square 20cm on a side. The sheets are separated by a distance of 1.0 mm. Show all your work and include units in your answers for full credit.

a) What is the capacitance of this capacitor?

b) The capacitor is connected to an unknown voltage source, and 5.0 nC of charge accumulates on each plate. What is the unknown voltage across the plates?

c) What is the magnitude of the electric field between the plates when it is charged as in part (b)? Remember that electric field can be expressed in units of V/m.

Explanation / Answer

a)

Area of aluminium foil

A=L2 =0.22 =0.04 m2

Capacitance

C=eoA/d =(8.85*10-12)*(0.04)/(1*10-3)

C=3.54*10-10 F or 0.354 nF or 354 pF

b)

V=Q/C =(5*10-9)/(3.54*10-10)

V=14.12 Volts

c)

E=V/d =14.12/(1*10-3)

E=14124.3 V/m

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