*Question E5C06:
What does the impedance 50 - j25 ohms represent?*  

*Correct Answer is  B: 50 ohms resistance in series with 25 ohms capacitive reactance*  

### AI Response: (may contain errors)  

In this question, we are dealing with complex impedance, which is expressed in the form $R + jX$, where:

- $R$ is the resistance (real part).
- $X$ is the reactance (imaginary part).
- $j$ is the imaginary unit, equivalent to $\sqrt{-1}$.

The given impedance is $50 - j25$ ohms. Let's break it down:

1. **Real Part (Resistance):**  
   - The real part is $50$ ohms, which represents the resistance.

2. **Imaginary Part (Reactance):**  
   - The imaginary part is $-j25$ ohms. The negative sign indicates capacitive reactance. Capacitive reactance is represented as $-jX_C$, where $X_C$ is the capacitive reactance in ohms.

Now, let's evaluate the choices:

- **Choice A: 50 ohms resistance in series with 25 ohms inductive reactance**  
  This is incorrect because inductive reactance is represented by a positive imaginary part ($+jX_L$), not negative.

- **Choice B: 50 ohms resistance in series with 25 ohms capacitive reactance**  
  This is correct. The negative imaginary part ($-j25$) indicates capacitive reactance.

- **Choice C: 25 ohms resistance in series with 50 ohms inductive reactance**  
  This is incorrect because the resistance is 50 ohms, not 25 ohms, and the reactance is not inductive.

- **Choice D: 25 ohms resistance in series with 50 ohms capacitive reactance**  
  This is incorrect because the resistance is 50 ohms, not 25 ohms.

**Key Rule of Thumb:**

- Positive imaginary part ($+jX$) indicates inductive reactance.
- Negative imaginary part ($-jX$) indicates capacitive reactance.

Thus, the correct answer is **B: 50 ohms resistance in series with 25 ohms capacitive reactance**.