Physics - Current Electricity Question with Solution | TestHub

The equlvalent circuit for the given electrical network isThis is a balanced Wheatstone bridge, so the arm containing $2r$ not in use. So, we haveSo, the equivalent resistance between a and bis $$\frac{1}{r^{\prime }}=\frac{1}{2r}+\frac{1}{2r}\Rightarrow r^{\prime }=\frac{2r}{2}=r$$