how does the light of a nephelometer determine the scatter of particles?

Answer 1

The particles scatter light, some of it goes to a photocell, the photocell generates a current when the photons strike the photosensitive cathode, an amplifier circuit then generates enough current to move a meter. Here is a web page you can read about it.
http://en.wikipedia.org/wiki/Nephelometer

Answer 2

thank you for your help