*Question G7C12:
What is the frequency above which a low-pass filter’s output power is less than half the input power?*  

*Correct Answer is  C: Cutoff frequency*  

### AI Response: (may contain errors)  

In this question, we are dealing with the concept of a low-pass filter, which is a type of electronic filter that allows signals with a frequency lower than a certain cutoff frequency to pass through and attenuates frequencies higher than this cutoff.

### Explanation:

1. **Correct Answer: Cutoff frequency (C)**
   - The **cutoff frequency** is the frequency at which the output power of a filter is reduced to half of the input power. This corresponds to a -3 dB point in the filter's frequency response. In terms of power, this is where the output power is 50% of the input power, or:
     $$ \text{Output Power} = \frac{1}{2} \times \text{Input Power} $$
   - This is a key characteristic of filters and is used to define the boundary between passband and stopband.

2. **Why the other choices are incorrect:**
   - **Notch frequency (A):** This refers to the frequency at which a notch filter significantly attenuates a narrow band of frequencies. It is not related to the half-power point of a low-pass filter.
   - **Neper frequency (B):** This term is not commonly used in the context of low-pass filters. It is more related to the concept of attenuation in terms of nepers, a logarithmic unit of ratio.
   - **Rolloff frequency (D):** While "rolloff" describes how quickly a filter attenuates frequencies beyond the cutoff, it is not specifically the point where the output power is half of the input power.

### Key Formula:

- The cutoff frequency is where the power is reduced to half, which corresponds to a -3 dB point:
  $$ \text{Power Ratio (dB)} = 10 \log_{10} \left( \frac{\text{Output Power}}{\text{Input Power}} \right) = -3 \, \text{dB} $$

Understanding the cutoff frequency is crucial for designing and analyzing filters in radio and electronic circuits.