# Homework Help: Capacitor and displacement current.

1. Feb 21, 2013

### altamashghazi

1. The problem statement, all variables and given/known data

a capacitor of capacitance 'C' is being charged across a dc source with an ammeter . will the ammeter show a momentary deflection during the process of charging? if so, how would it and the resulting continuity of current in the circuit be explained ?

2. Relevant equations

maxwell's displacement current equation

3. The attempt at a solution

continuity is bcoz conduction +displacement current is same everywhere in circuit but what about momentary deflection ?

2. Feb 22, 2013

### Basic_Physics

You basically have a RC circuit with very little resistance so that the voltage over the capacitor , VC,will build up very fast during the charging process according to

VC = E(1 - e-t/RC)

where E is the emf of the dc source. The voltage of the capacitor opposes that of the dc source and the current will stop when the two voltages are the same - that is the charging process stops. The charge build up on the capacitor will be

q = CVC

so that the current will be decaying exponentially with time

i = dq/dt = E/R e-t/RC