FCC Exam Question: 6A87

The total inductance of two coils in parallel without any mutual coupling is:

A. Equal to the product of the two inductances divided by their sum
B. The sum of the individual inductances
C. Zero
D. None of the above
Correct Answer: A

Explanation: When two inductors are connected in parallel without mutual coupling, their total inductance is calculated using the product-over-sum formula: $L_{total} = (L_1 \times L_2) / (L_1 + L_2)$. This is derived from the general reciprocal sum formula: $1/L_{total} = 1/L_1 + 1/L_2$. **A) Equal to the product of the two inductances divided by their sum** is correct because connecting inductors in parallel provides alternative paths for current. This effectively reduces the overall opposition to changes in current, similar to how parallel resistors reduce total resistance. The total inductance will always be less than the smallest individual inductance. **B) The sum of the individual inductances** is incorrect. This formula ($L_{total} = L_1 + L_2$) applies when inductors are connected in *series*, where their magnetic fields add up to create a greater total opposition. **C) Zero** is incorrect. Two physical coils will always have some non-zero inductance, which measures their ability to oppose changes in current. **D) None of the above** is incorrect because option A is the correct method for calculating total inductance in a parallel circuit.

Pass Your FCC Exam!

Study offline, track your progress, and simulate real exams with the GMDSS Trainer app.


Includes Elements 1, 3, 6, 7R, 8, and 9.