Conceptual Exercise 21.76 Part A Three RC circuits have the emf, resistance, and

Question

Conceptual Exercise 21.76 Part A Three RC circuits have the emf, resistance, and capacitance given in the accompanying table. Initially the switch on the circuit is open and the capacitor is uncharged. Rank these circuits in order of decreasing initial current (immediately after the switch is closed Rank from largest to smallest. To rank items as equivalent, overlap them. Reset Help E(V) | R (n) | C (pE) Cruit A1243 Circuit B9 Circuit C 9 Circuit A Circuit B CircuitC Largest Smallest The correct ranking cannot be determined. Submit My Answers Give Up

Explanation / Answer

Part A:

Since the caps are discharged, the only impedance to flow INITIALLY is the resistors! So initially, current flow is:

I(A) = 12V/4ohms = 3A
I(B) = 9V/3ohms = 3A
I(C) = 9V/9ohms = 1A

A and B are tied for first, with C next.

Part B:

The time to charge up depends on the 'time constant' = CR
The time constant relative values are : A = 12, B = 3, C =18
So the decreasing times are : C A B

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