Circuits question

[MalibuPreMD]

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The question refers to a picture of a circuit where resistor x is in series with resistor y and a capacitor (Ry and C are in parallel). Thequestion asks: adding a third resistor in such a way that it was in parallel to both ryand the capacitor would:

a) increase thecurrent through rx.
b) decrease the current through ry
c) increase the capacitance of c
d) decrease the total power drain of the circuit


I wrongly put b. The correct answer is a. How can this be? I feel like the question has to be wrongly worded.

 

[BerkReviewTeach]

The question refers to a picture of a circuit where resistor x is in series with resistor y and a capacitor (Ry and C are in parallel). Thequestion asks: adding a third resistor in such a way that it was in parallel to both ryand the capacitor would:

a) increase thecurrent through rx.
b) decrease the current through ry
c) increase the capacitance of c
d) decrease the total power drain of the circuit


I wrongly put b. The correct answer is a. How can this be? I feel like the question has to be wrongly worded.

Parallel paths are independent, so adding another circuit element in parallel has no effect whatsoever on the preexisting parallel circuit elements. In other words, the current going through Ry and across the capacitor will not be affected by the addition of the new resistor in parallel.

However, more current can now pass through the parallel set of circuit elements (adding a resistor in parallel will lower the equivalent resistance), so according to Kirkhoff's junction rule, more current is entering the junction. This means that more current is leaving the cathode, passing through Resistor X, and arriving at the anode. The current through Rx must increase.

 

[paul411]

Current won't flow through the capacitor so we can ignore it.

Resistor ry and r3 are now in parallel. Let's assume they're equivalent, the resultant resistance is ry/2 (less than the original resistance). Hence, more current flows through the circuit (also through rx)

 

[paul411]

Parallel paths are independent, so adding another circuit element in parallel has no effect whatsoever on the preexisting parallel circuit elements. In other words, the current going through Ry and across the capacitor will not be affected by the addition of the new resistor in parallel.

However, more current can now pass through the parallel set of circuit elements (adding a resistor in parallel will lower the equivalent resistance), so according to Kirkhoff's junction rule, more current is entering the junction. This means that more current is leaving the cathode, passing through Resistor X, and arriving at the anode. The current through Rx must increase.

I like this answer better.