Unbalanced Wheatstone Bridge voltage across resisitors

1. Sep 1, 2011

msslowlearner

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

It is a qualitative problem. No values are given.
In an unbalanced Wheatstone Bridge, does the voltage across the resistors R4 and R2 change? In other words is Vr2of balanced bridge=Vr2 of unbalanced bridge? likewse for R4.

2. Relevant equations

The Bridge Balance eqn is R1/R2 = R3/R4, where R4 is the variable resistor. At balanced condition, Vr2 = Vr4

3. The attempt at a solution
The change in Vr4 is obvious. My problem was why does Vr2 remain constant??
I assumed that as current flows through R1 - Rg - R4 path, the current through R1 is also changing. But the current through R2 does not change as the extra Ig doesn't come into R2. I thought this was the reason behind Vr2 being constant.

But, the text said "the current through R1 doesn't change with change in R4. Hence, Vr2 does not change" .... How ?? I dont understand.. Is the text trying to say the current in the R1-R2 arm doesn't change at all ? Then what is the path of Ig from the source ??

2. Sep 1, 2011