*Question G5A11:
What letter is used to represent reactance?*  

*Correct Answer is  B: X*  

### AI Response: (may contain errors)  

In electrical engineering and amateur radio, reactance is represented by the letter $X$. Reactance is a component of impedance that accounts for the opposition to the change in current by inductors and capacitors in an AC circuit.

1. **Correct Answer: X**
   - The letter $X$ is used to denote reactance. Reactance can be either inductive ($X_L$) or capacitive ($X_C$), and it is measured in ohms ($\Omega$).

2. **Why the Other Choices are Incorrect:**
   - **A: Z**  
     - $Z$ represents impedance, which is the total opposition to current flow in an AC circuit. Impedance is a combination of resistance ($R$) and reactance ($X$), expressed as $Z = R + jX$.
   - **C: B**  
     - $B$ is not typically used to represent reactance. In some contexts, $B$ can represent susceptance, which is the reciprocal of reactance.
   - **D: Y**  
     - $Y$ is used to represent admittance, which is the reciprocal of impedance.

3. **Useful Formulas:**
   - Inductive Reactance: $X_L = 2\pi f L$, where $f$ is the frequency in hertz and $L$ is the inductance in henrys.
   - Capacitive Reactance: $X_C = \frac{1}{2\pi f C}$, where $C$ is the capacitance in farads.

Understanding these symbols and their meanings is crucial for analyzing and solving AC circuit problems in the Extra Class exam.