Hi all, I'm having an issue with Question 33 on this worksheet: http://www.allaboutcircuits.com/worksheets/dc_sp.html

I understand why the effects occur in R1, R3 and R4 but why does the voltage dropped across R2 decrease? Isn't the voltage in a parallel circuit equally dropped? So if Vr3 increases and Vr4 decreases doesn't that balance out and leave Vr2 unaffected or at least increased voltage dropped?

Help is much appreciated.

 

R2 is in parallel with R4 and R3 which are in series. So the same voltage drop you have on R3 - R4 you have on R2. Decreasing the resistance by shorting R4 will decrease the total voltage drop on R3 - R4, therefore decrease the voltage drop on R2.

You increase the current through R1 but this current is then divided into to branches, so this does not balance out.

I think the easiest is to put real values in the circuit and then calculate what happens.

 

Thanks a lot! The reason I didn't put real values into the circuit was due to the problem being a test of qualitative analysis.