Question

Thirteen resistances each of resistance $R$ ohm are connected in the circuit as shown in the figure below. The effective resistance between $A \, and \, B$ is

• A. $R\Omega $
• B. $\frac{2 R}{3} \, \Omega $
• C. $\frac{4 R}{3}\Omega $
• D. $2R\Omega $

Answer 1

Answer: (B)

Equivalent circuit will be

Now above circuit is a wheat stone's bridge.
By solving we get.
$R_{A B}=\frac{\frac{4}{3} R \times \frac{4}{3} R}{\frac{4}{3} R + \frac{4}{3} R}=\frac{2}{3}R$