*Question G5A09:
What unit is used to measure reactance?*  

*Correct Answer is  B: Ohm*  

### AI Response: (may contain errors)  

Reactance is a component of impedance in an AC circuit, and it is measured in ohms. Here's why:

1. **Correct Answer: Ohm**
   - Reactance, like resistance, is a measure of opposition to current flow, but it specifically applies to AC circuits. It is part of the total impedance, which is the combination of resistance and reactance. Since impedance is measured in ohms, reactance is also measured in ohms.

2. **Why the Other Choices are Incorrect:**
   - **Farad (A):** This is the unit of capacitance, not reactance. Capacitance is a property of capacitors, which store electrical energy.
   - **Ampere (C):** This is the unit of electric current, not reactance. Current is the flow of electric charge.
   - **Siemens (D):** This is the unit of conductance, which is the reciprocal of resistance, not reactance.

3. **Useful Formulas:**
   - The reactance of a capacitor ($X_C$) is given by:
     $$X_C = \frac{1}{2\pi f C}$$
     where $f$ is the frequency in hertz and $C$ is the capacitance in farads.
   - The reactance of an inductor ($X_L$) is given by:
     $$X_L = 2\pi f L$$
     where $L$ is the inductance in henrys.

Both $X_C$ and $X_L$ are measured in ohms, reinforcing that reactance is indeed measured in ohms.