*Question E4B08:
Which of the following can be used to determine the Q of a series-tuned circuit?*  

*Correct Answer is  C: The bandwidth of the circuit's frequency response*  

### AI Response: (may contain errors)  

To determine the Q (quality factor) of a series-tuned circuit, the correct answer is:

**C: The bandwidth of the circuit's frequency response.**

### Explanation of the Correct Answer:
- The Q factor is defined as the ratio of the resonant frequency ($f_0$) to the bandwidth ($BW$) of the circuit. It indicates how selective the circuit is at its resonant frequency.
  
The formula for Q is given by:

$$
Q = \frac{f_0}{BW}
$$

Where:
- $f_0$ = resonant frequency
- $BW$ = bandwidth (the range of frequencies over which the circuit can operate effectively)

A higher Q indicates a narrower bandwidth and better selectivity.

### Why the Other Choices are Incorrect:
- **A: The ratio of inductive reactance to capacitive reactance**  
  This ratio does not directly provide the Q factor. While it relates to the impedance of the circuit, it does not account for the bandwidth or the energy losses in the circuit.

- **B: The frequency shift**  
  Frequency shift refers to changes in the resonant frequency due to various factors (like component tolerances or loading effects). It does not provide information about the Q factor or the bandwidth.

- **D: The resonant frequency of the circuit**  
  While the resonant frequency is a component of the Q factor formula, it alone does not determine the Q. The Q factor requires knowledge of the bandwidth as well.

### Summary:
- The Q factor is best determined using the bandwidth of the circuit's frequency response, making option C the correct choice. Understanding the relationship between resonant frequency and bandwidth is crucial for calculating Q effectively.