Question

The net resistance between the points $P$ and $Q$ in the circuit shown in the figure is:

• A. $R/2$
• B. $2R/5$
• C. $3R/5$
• D. $R/3$

Answer 1

The correct option is B $2R/5$

One end of the leftmost and rightmost resistors are earthed and hence are at same potential and hence can be joined end to end.

In last step there are three parallel resistances $R,2R,$ and $R$.

For, equivalent resistance:-

$\frac{1}{R_{eq}}=\frac{1}{R}+\frac{1}{2R}+\frac{1}{R}$

$=\frac{2+1+2}{2R}=\frac{5}{2R}$

$⟹R_{eq}=\frac{2R}{5}$

Answer-(B)