How to find range with height and velocity

What is the thinnest soap film (excluding the case of zero thickness) that appears black when illuminated with light with a wavelength of 480 ? the index of refraction of the film is 1.34, and there is air on both sides of the film. express your answer in nanometers. hint 1. how to approach th

Give one example to show that when substances are mixed, it may result in a chemical or a physical change depending on the conditions.

What is the major limitation to the light microscope?