*Question G5A03:
Which of the following is opposition to the flow of alternating current in an inductor?*  

*Correct Answer is  D: Reactance*  

### AI Response: (may contain errors)  

To understand the opposition to the flow of alternating current (AC) in an inductor, we need to focus on the concept of reactance.

1. **Correct Answer: Reactance**
   - Reactance is the opposition to the flow of AC due to inductance or capacitance. For an inductor, the reactance ($X_L$) is given by the formula:
   $$
   X_L = 2 \pi f L
   $$
   where:
   - $f$ = frequency of the AC signal in hertz (Hz)
   - $L$ = inductance in henries (H)
   - This formula shows that as frequency increases or inductance increases, the reactance also increases, leading to greater opposition to the current flow.

2. **Why the Other Choices are Incorrect:**
   - **A: Conductance**
     - Conductance is the measure of how easily electricity flows through a conductor, and it is the reciprocal of resistance. It does not apply to the opposition caused by inductors in AC circuits.
   - **B: Reluctance**
     - Reluctance is a term used in magnetic circuits, analogous to resistance in electrical circuits. It measures the opposition to magnetic flux, not to the flow of AC in an inductor.
   - **C: Admittance**
     - Admittance is the measure of how easily a circuit allows current to flow, and it is the reciprocal of impedance. While it relates to AC circuits, it does not specifically refer to the opposition caused by inductors.

3. **Useful Formulas and Rules of Thumb:**
   - For inductors, remember that the reactance increases with frequency:
   $$
   X_L = 2 \pi f L
   $$
   - In AC circuits, total opposition to current flow is called impedance ($Z$), which combines resistance ($R$) and reactance ($X$):
   $$
   Z = \sqrt{R^2 + X^2}
   $$

Understanding these concepts will help you grasp how inductors behave in AC circuits and prepare you for related questions on the Extra Class exam.