*Question E5C11:
Which point in Figure E5-1 best represents the impedance of a series circuit consisting of a 300-ohm resistor and an 18-microhenry inductor at 3.505 MHz?*  

*Correct Answer is  B: Point 3*  

### AI Response: (may contain errors)  

To determine the impedance of a series circuit consisting of a 300-ohm resistor and an 18-microhenry inductor at a frequency of 3.505 MHz, we need to calculate the total impedance, which is the sum of the resistive and reactive components.

1. **Calculate the inductive reactance ($X_L$)**:  
   The inductive reactance can be calculated using the formula:  
   $$X_L = 2 \pi f L$$  
   where:
   - $f$ = frequency in hertz (Hz)
   - $L$ = inductance in henries (H)

   For our case:  
   - $f = 3.505 \, \text{MHz} = 3.505 \times 10^6 \, \text{Hz}$
   - $L = 18 \, \mu H = 18 \times 10^{-6} \, H$

   Plugging in the values:  
   $$X_L = 2 \pi (3.505 \times 10^6) (18 \times 10^{-6})$$  
   $$X_L \approx 0.398 \, \Omega$$

2. **Total impedance ($Z$)**:  
   The total impedance in a series circuit is given by:  
   $$Z = R + jX_L$$  
   where:
   - $R$ = resistance (300 ohms)
   - $j$ = imaginary unit

   Thus, the impedance becomes:  
   $$Z = 300 + j0.398$$

3. **Magnitude of the impedance**:  
   The magnitude of the impedance can be calculated as:  
   $$|Z| = \sqrt{R^2 + X_L^2}$$  
   $$|Z| = \sqrt{300^2 + 0.398^2} \approx 300 \, \Omega$$  
   Since the inductive reactance is very small compared to the resistance, the impedance is approximately equal to the resistance.

### Explanation of the Correct Answer (Point 3):
- **Point 3** represents a high impedance value close to 300 ohms, which aligns with our calculated impedance. The small inductive reactance does not significantly affect the overall impedance in this case.

### Why Other Choices Are Incorrect:
- **Point 1**: Likely represents a much lower impedance, which does not match our calculated value.
- **Point 7**: May indicate a purely reactive impedance or a much higher impedance, which is not consistent with our findings.
- **Point 8**: Similar to Point 7, it likely represents an impedance that is not close to 300 ohms.

### Summary:
- The impedance of the series circuit is approximately 300 ohms due to the dominant resistive component, with a negligible inductive reactance. Thus, Point 3 is the correct representation of the impedance at the given frequency.