*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)  

The impedance $50 - j25$ ohms can be analyzed as follows:

1. **Understanding Impedance**: 
   - Impedance is represented in the form $R + jX$, where $R$ is the resistance (real part) and $X$ is the reactance (imaginary part).
   - A positive imaginary part ($jX$) indicates inductive reactance, while a negative imaginary part ($-jX$) indicates capacitive reactance.

2. **Analyzing $50 - j25$ ohms**:
   - Here, $R = 50$ ohms (resistive part) and $X = -25$ ohms (reactive part).
   - Since the reactance is negative, this indicates that the impedance represents capacitive reactance.

3. **Correct Answer**:
   - The correct answer is **A**: 50 ohms resistance in series with 25 ohms capacitive reactance. This is because the impedance can be interpreted as a 50-ohm resistor in series with a capacitor that has a reactance of 25 ohms.

4. **Why Other Choices are Incorrect**:
   - **B**: 50 ohms resistance in series with 25 ohms capacitive reactance - Incorrect because it states capacitive reactance as positive.
   - **C**: 25 ohms resistance in series with 50 ohms inductive reactance - Incorrect because it misrepresents the values and the sign of the reactance.
   - **D**: 25 ohms resistance in series with 50 ohms capacitive reactance - Incorrect for the same reason as C; it misrepresents the values and the sign.

5. **Useful Formulas and Rules of Thumb**:
   - For impedance $Z = R + jX$:
     - If $X > 0$, the circuit is inductive.
     - If $X < 0$, the circuit is capacitive.
   - The magnitude of the impedance can be calculated as:
   $$|Z| = \sqrt{R^2 + X^2}$$

This understanding of impedance will help you in various exam questions related to AC circuits and reactance.