Question

The equivalent resistance between the points $a$ and $b$ of the electrical network shown in the figure is

• A. 6 r
• B. 4 r
• C. 2 r
• D. r

Answer 1

Answer: (D)

The equivalent circuit for the given electrical network is

This is a balanced Wheatstone bridge, so the arm containing $2r$ not in use. So, we have

So, the equivalent resistance between $a$ and $b$ is
$\frac{1}{r^{\prime }}=\frac{1}{2r}+\frac{1}{2r}$
$\Rightarrow r^{\prime }=\frac{2r}{2}=r$