The equivalent resistance between the points $A$ and $B$ will be (each resistance is $15 \Omega$ )

• A

  $30 \Omega$
• Correct answer
  B

  $8 \Omega$
• C

  $10 \Omega$
• D

  $40 \Omega$

Solution

Redrawing the given circuit network as

Equivalent resistance between points $D$ and $C$, $$ R_{D C}=\frac{(15+15) \times 15}{(15+15)+15}=\frac{30 \times 15}{45}=10 \Omega $$ Similarly, $\quad R_{A B}=R_{D C}=10 \Omega$ Now, circuit, diagram reduces as

$\therefore$ Equivalent resistance between points $A$ and $B$ is given as $$ \begin{aligned} R_{A B}=(15+10+15)\|10=40\| 10 &=\frac{40 \times 10}{40+10} \\ &=\frac{400}{50}=8 \Omega \end{aligned} $$

Hence, the correct answer is option: 'B'.