Electronic – Trouble finding the R(equivalent) in this circuit

circuit analysisresistanceresistors

I started studying Electric Circuits one week ago so this material is new to me. I was trying to solve this problem from the book but I had some difficulty:

enter image description here

My analysis:

The equivalent resistance R1 for parallel resistors 16Ω and 48Ω is 12Ω (16×48/16+48).

The equivalent resistance R2 for parallel resistors 24Ω and 12Ω is (24×12/24+12).

The equivalent resistance R3 for resistors in series R2 and 22Ω is 30Ω (8+22).

The equivalent resistance R4 for parallel resistors R3 and 45Ω is 18Ω (30×45/30+45).

The equivalent resistance Rab for resistors in series R1 and 18Ω is 30Ω (12+18).

Why is the final answer 34Ω? Mine got 30Ω.

Best Answer

Your book is wrong, and you are right:


simulate this circuit – Schematic created using CircuitLab

Try to simulate that, and you will get that the voltage across the current generator is 30V, i.e. the resistance seen by the current generator is \$\frac{30}{1}\Omega=30\Omega\$.

This trick is very useful when you have tons of exercises with no solution, plus you learn how to use a simulator (use some spice flavour). Of course you should always solve the exercise by hand and, if you are not sure your result is correct, check it with the simulator. Learning how to deal with circuits without the help of a computer is a necessary base for an EE, don't be too attracted by the simulator.