Question

Consider an air filled parallel plate capacitor with one plate connected to a spring having a force constant k and the other plate is held fixed. The system rests on frictionless table top. The plates have charge density σ and -σ, area A, charges Q and -Q. The electrostatic force due to the electric field created by the plate b is Fe and the spring gets an extension x . Then  

Answer 1

Correct option: (a,b,c)

Explanation:

Similarly, the electrostatic force vector Fe due to the electric field created by plate b is

where A is the area of the plate. Notice that charges on plate a cannot exert a force on itself, as required by Newton’s Third Law. Thus, only the electric field due to plate b is considered. At equilibrium the two forces cancel and we have