Answer
a. The equivalent resistance is $4 \Omega$.
b. 6 A.
c. 2 A.
Work Step by Step
a. A pair of resistors wired in series has an equivalent resistance equal to the sum of the resistances. This is Rule 2 on page 443.
The top branch then has an equivalent resistance of $12 \Omega$ and so does the bottom branch. We now effectively have three $12 \Omega$ resistors in parallel.
The equation is not given in this textbook, but for 3 resistors in parallel, the following relation holds.
$$\frac{1}{R_{parallel}} = \frac{1}{R_{1}} + \frac{1}{R_{2}} + \frac{1}{R_{3}} $$
Apply the equation to this problem.
$$\frac{1}{R_{parallel}} = 3 \times \frac{1}{12 \Omega} = \frac{1}{4 \Omega} $$
$$R_{parallel} = 4 \Omega$$
b. $I = \frac{V}{R} = \frac{24V}{4 \Omega} = 6 A$.
c. $I = \frac{V}{R} = \frac{24V}{12 \Omega} = 2 A$.
