Question

find Rab, effective resistance​

Answer 1

Answer:

here is the answer:

The first observation is that the circuit is symmetric. I will come back to why this is important.

Lets say current I enters at point a and exits at b. I divides into 2 parts Ih [ horizontal ] and Iv [ vertical ]. Since the circuit is symmetrical point a and b are interchangeable hence there will be no current in the first middle horizontal resistor.

Extending the same logic , there will be no current in the next middle horizontal resistor. So we can remove them from the circuit.

Now, the circuit is simplified and the final Rab is :

R1 = 8||4 Ohms

R2 = 4||(4+R1) Ohms

Rab = 4 + R2 Ohms

Explanation:

hope it's helpful......