Question

The resistance of all the wires between any two adjacent dots is $R$.Then equivalent resistance between $A$ and $B$ as shown in figure is :

• A. $7/3R$
• B. $7/6R$
• C. $14/8R$
• D. $Noneofthese$

Answer 1

The correct option is B $7/6R$

Considering the for triangles of the star, in each triangle the are 2 resistors in series which in turn are connected in parallel with another resistor

So we get its equivalent resistance as $\frac{2R}{3}$

Now in between A and B there are 2 resistances connected in parallel and each resistance is equal to $(\frac{2R}{3}+\frac{2R}{3}+R)=\frac{7R}{3}$

So$\frac{1}{R_{eq}}=\frac{3}{7R}+\frac{3}{7R}$

$R_{eq}=\frac{7R}{6}$