Problem + Hard 55-2    Source:   Question 1 - List 1st area - Discipline Electrical Circuits of the School of Engineering - UFRGS - 1972 - Prof. doctor Sérgio Machado Bordini.

Solution of the Problem + Hard 55-2

Solution presented by the author in his book and adapted by the author of the website.

So that there is a potential difference between the terminals a-b of 50 volts and, knowing that a current flows equal to 10 A by the equivalent impedance connected to these terminals, then it is possible to calculate this equivalent impedance, or:

Therefore, the parallel of the four elements connected to the a-b terminals must be equivalent to a 5 ohm resistor. Working with admittances we can write:

Carrying out the calculations, we get:

That is, the X element must be a capacitor (due to the negative sign) whose reactance must present a value equal to 10 ohms.