*Question E5C01:
Which of the following represents pure capacitive reactance of 100 ohms in rectangular notation?*  

*Correct Answer is  A: 0 - j100*  

### AI Response: (may contain errors)  

In electrical engineering, reactance is a measure of how much a component resists the change in current. Reactance can be either inductive or capacitive, and it is represented in complex numbers using rectangular notation.

### Explanation:

1. **Capacitive Reactance:**
   - Capacitive reactance is represented as a negative imaginary number in rectangular notation.
   - The formula for capacitive reactance is $X_C = -jX$, where $X$ is the magnitude of the reactance in ohms and $j$ is the imaginary unit.

2. **Correct Answer: 0 - j100**
   - This represents a pure capacitive reactance of 100 ohms.
   - The real part is 0, indicating no resistance, and the imaginary part is $-j100$, indicating capacitive reactance.

3. **Why Other Choices Are Incorrect:**
   - **A: 0 - j100**: Correct, as explained above.
   - **B: 0 + j100**: This represents inductive reactance, not capacitive, because the imaginary part is positive.
   - **C: 100 - j0**: This represents pure resistance of 100 ohms, with no reactance.
   - **D: 100 + j0**: This also represents pure resistance of 100 ohms, with no reactance.

### Key Points:
- **Capacitive Reactance** is always represented with a negative imaginary component.
- **Inductive Reactance** would have a positive imaginary component.
- **Resistance** is represented by the real part of the complex number, with no imaginary component.

Understanding these concepts will help you correctly identify and differentiate between capacitive and inductive reactance in exam questions.