Solve Circuit for R(ab): Equivalent Resistance 20 Ohms?

[jonathan.15]

The question asks to find the Equivalent resistance R(ab) for the circuit. Is this a trick question? Because I thought it is an open circuit and therefore the resistance between a and b would be infinite. The answer in the book is 20 ohms, please explain if possible

 

[AlephZero]

Why do you think the resistance is infinite? There are lots of ways the current can flow from a to b.

You can solve this by picking off pairs of resistors that are in series and parallel, and replacing then with a single resistor. You will end up with just one resistor connecting a and b.

 

[jonathan.15]

Because there is no wire connecting points A and B I thought this is an open circuit, which has infinite resistance?

 

[jonathan.15]

This is my final step in reducing the circuit, so now this makes sense that the resistance would be 20, I kept thinking that current would not flow flow from a down to b because they were separated but they are connected

 

[Redbelly98]

Moderator's note: thread moved from Electrical Engineering.