*Question E5C07:
Where is the impedance of a pure resistance plotted on rectangular coordinates?*  

*Correct Answer is  D: On the horizontal axis*  

### AI Response: (may contain errors)  

To understand where the impedance of a pure resistance is plotted on rectangular coordinates, we need to consider the representation of impedance in the complex plane.

1. **Correct Answer: On the horizontal axis**  
   - Impedance ($Z$) is represented as a complex number:  
   $$Z = R + jX$$  
   where:
   - $R$ = resistance (real part)
   - $X$ = reactance (imaginary part)
   - For a pure resistance, the reactance $X = 0$.  
   - Therefore, the impedance is purely real and can be plotted as a point on the horizontal axis (real axis) of the complex plane.

2. **Why the other choices are incorrect:**
   - **A: On the vertical axis**  
     - This would represent a purely reactive component (pure inductance or capacitance), where $R = 0$ and $X \neq 0$. This is not applicable for pure resistance.
   - **B: On a line through the origin, slanted at 45 degrees**  
     - A 45-degree line represents equal real and imaginary components (i.e., $R = X$). This does not apply to pure resistance, where $X = 0$.
   - **C: On a horizontal line, offset vertically above the horizontal axis**  
     - This would imply a complex impedance with a non-zero imaginary part (reactance), which is not the case for pure resistance.

3. **Useful Formulas or Rules of Thumb:**
   - Remember that in the complex plane:
     - The horizontal axis represents the real part (resistance).
     - The vertical axis represents the imaginary part (reactance).
   - For any impedance $Z$, if $X = 0$, then $Z$ lies on the horizontal axis.

This understanding will help you visualize and interpret impedance in various circuit scenarios, especially in the context of the Extra Class exam.