How to derive low pass filter $\frac{N}{N+S}$

1. How do you find a low pass filter?
2. How do you define a low pass filter?

How do you find a low pass filter?

Filters can be placed into broad categories that correspond to the general characteristics of the filter's frequency response. If a filter passes low frequencies and blocks high frequencies, it is called a low-pass filter. If it blocks low frequencies and passes high frequencies, it is a high-pass filter.

How do you define a low pass filter?

A low-pass filter (LPF) is a circuit that only passes signals below its cutoff frequency while attenuating all signals above it. It is the complement of a high-pass filter, which only passes signals above its cutoff frequency and attenuates all signals below it.