*Question G5A02:
What is reactance?*  

*Correct Answer is  B: Opposition to the flow of alternating current caused by capacitance or inductance*  

### AI Response: (may contain errors)  

Reactance is a concept in AC (alternating current) circuits that describes how capacitors and inductors oppose the flow of current. Here's a breakdown of the correct answer and why the other choices are incorrect:

1. **Correct Answer: B - Opposition to the flow of alternating current caused by capacitance or inductance**

   - **Explanation**: Reactance is the resistance to the change in current flow in an AC circuit due to capacitors and inductors. It is frequency-dependent, meaning it varies with the frequency of the AC signal.
   - **Capacitive Reactance** ($X_C$): This is the opposition to current flow by a capacitor and is given by the formula:
     $$X_C = \frac{1}{2\pi f C}$$
     where $f$ is the frequency in hertz and $C$ is the capacitance in farads.
   - **Inductive Reactance** ($X_L$): This is the opposition to current flow by an inductor and is given by the formula:
     $$X_L = 2\pi f L$$
     where $L$ is the inductance in henrys.

2. **Why the other choices are incorrect:**

   - **Choice A**: Opposition to the flow of direct current caused by resistance
     - **Explanation**: This describes resistance, not reactance. Resistance is the opposition to current flow in both AC and DC circuits and is not frequency-dependent.
   
   - **Choice C**: Reinforcement of the flow of direct current caused by resistance
     - **Explanation**: Resistance does not reinforce current flow; it opposes it. This statement is incorrect as it mischaracterizes the role of resistance.
   
   - **Choice D**: Reinforcement of the flow of alternating current caused by capacitance or inductance
     - **Explanation**: Capacitance and inductance do not reinforce current flow; they oppose it in AC circuits, which is why they are described by reactance.

Understanding reactance is crucial for analyzing AC circuits, as it affects how capacitors and inductors influence the circuit's impedance and phase relationships.