Problem 2.7   Source:   Problem elaborated by the author of the site.

Calculate the equivalent resistance between the points a-b of the circuit shown in Figure 02-07.1.

Solution of the Problem 2.7

Note that the resistors of values equal to 16 Ω and 14 Ω, between points 1 - 2 - 3, are in series, resulting in a equivalent resistance with a value of 16 + 14 = 30 ohms. And this resistance is in parallel with the resistor of 20 ohms which is between points 1 - 3 . Solving this parallel we find as a result the value of 12 ohms which is the resistance equivalent value between points 1 - 3 . Of course this equivalent resistance of 12 ohms is in series with the resistance of 18 ohms which is between points 3-4. So, by adding their values we have an equivalent resistance of 30 ohms , which is the equivalent resistance of the branch passing through the points 1-2-3-4. Thus, between points 1-4 results in a parallel of two resistors of 30 ohms. So the equivalent resistance between points 1 - 4 is:

And now it is evident that R₁₄ is in series with the other two resistors of the circuit, that of 10 ohms and 25 ohms, resulting in a three resistors series circuit. So just add the values of these resistors to find the equivalent resistance value between the points a - b. Soon: