Problem #0278 Electricity & Magnetism Sub-menu Problem #0280 Chapters Chapters

549.

Problem 40.14 (RHK)

A capacitor consisting of two circular plates with radius is connected to a source of emf , where and . The maximum value of the displacement current is . Neglecting fringing of the electric field at the edges of the plates, we have to find the maximum value of the current ; the maximum value of , where is the electric flux through the region between the plates; the separation between the plates d; and the maximum value of the magnitude of between the plates at a distance from the centre.

 

Solution:             Click For PDF Version

From the data of the problem we note that the emf applied across the plates of the capacitor can be described by the function

.

Let the separation between the plates be . Variation of the electric field between the plates will be given by the function

The displacement current is given in terms of the change of electric flux per unit time by the relation

The maximum value of will therefore be given by

It is given that

.

Therefore,

The maximum value of the charging current will be equal to the maximum value of the displacement current. Therefore, the maximum value of the charging current will be .

We will next calculate the separation between the plates.

We know that

Therefore,

We will find next the maximum value of between the plates at a distance from the centre. The Ampere’s law states that

Considering an Amperian circular loop of radius , we have