Q1. The resistance of a parallel circuit consisting of two branches is 12 ohm. If the resistance of one branch is 18 ohm, what is the resistance of the other?
A 18 ohm
B 36 ohm Correct
C 48 ohm
D 64 ohm
Explanation
For two resistors in parallel, the equivalent resistance is given by 1/R = 1/R1 + 1/R2. Here the equivalent resistance is 12 ohm and one branch is 18 ohm. Thus 1/12 = 1/18 + 1/R2, so 1/R2 = 1/12 - 1/18 = 1/36. Hence the other resistance is 36 ohm. A value of 18 ohm would give 9 ohm equivalent, while 48 ohm or 64 ohm would give equivalent values higher than 12 ohm.