# The parallel-plate air capacitor in Fig consists of two horizontal conducting plates of equal area A. The

## Question:

(a) Show that the electrostatic force between the charged plates has a magnitude є0Av2/2z2.

(b) Obtain an expression that relates the plate separation z to the potential difference V. The resulting equation will be cubic in z.

(c) Given the values A = 0.300 m2, Z0 = 1.20 mm, k = 25.0 N/m and V = 120 V, find the two values of z for which the top plate will be in equilibrium.

(d) For each of the two values of z found in part (c), is the equilibrium stable or unstable? For stable equilibrium a small displacement of the object will give rise to a net force tending to return the object to the equilibrium position. For unstable equilibrium a small displacement gives rise to a net force that takes the object farther away from equilibrium.

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**Related Book For**

## Vector Mechanics for Engineers Statics and Dynamics

**ISBN:** 978-0073212227

8th Edition

**Authors:** Ferdinand Beer, E. Russell Johnston, Jr., Elliot Eisenberg, William Clausen, David Mazurek, Phillip Cornwell