*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, you can use the bandwidth of the circuit's frequency response. Here's why:

### Correct Answer: C - The bandwidth of the circuit's frequency response

1. **Explanation**:  
   The quality factor, $Q$, of a series-tuned circuit is a measure of how "sharp" or "selective" the circuit is at its resonant frequency. It is defined as the ratio of the resonant frequency ($f_0$) to the bandwidth ($BW$) of the circuit:
   $$Q = \frac{f_0}{BW}$$
   - **Resonant Frequency ($f_0$)**: The frequency at which the circuit naturally oscillates.
   - **Bandwidth ($BW$)**: The range of frequencies over which the circuit can effectively operate, typically measured between the -3 dB points on the frequency response curve.

2. **Why Other Choices Are Incorrect**:
   - **A: The ratio of inductive reactance to capacitive reactance**  
     This ratio does not directly determine the Q of the circuit. Instead, it relates to the impedance characteristics at a specific frequency, not the overall quality factor.
   
   - **B: The frequency shift**  
     Frequency shift refers to a change in frequency, which is not directly related to the Q factor. Q is about the sharpness of the resonance, not shifts in frequency.
   
   - **D: The resonant frequency of the circuit**  
     While the resonant frequency is part of the formula for Q, knowing it alone does not determine Q. You need the bandwidth as well to calculate the quality factor.

### Summary

To find the Q of a series-tuned circuit, focus on the bandwidth of its frequency response. The narrower the bandwidth relative to the resonant frequency, the higher the Q, indicating a more selective circuit.