Question

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

• A. $30\Omega$
• B. $8\Omega$
• C. $10\Omega$
• D. $40\Omega$

Answer 1

The correct option is B $8\Omega$

Using the envelope theory , We can open the circuit from center

Let the center be O

$R_{DC}=\frac{1}{15}+\frac{1}{30}\to R_{DC}=10$

$R_{ADCB}=15+15+10=40$

$R_{AOB}=15+15=30$

$\frac{1}{R_{AB}}=\frac{1}{15}+\frac{1}{40}+\frac{1}{30}$

$R_{AB}=8$