Which phase of matter has a fixed volume, but variable shape?

What is the major limitation to the light microscope?

The illuminance of a surface varies inversely with the square of its distance from the light source. if the illuminance of a surface is 120 lumens per square meter when its distance from a certain light source is 6 meters, by how many meters should the distance of the surface from the source be increased to reduce its illuminance to 30 lumens per square meter?

The receptor cells that convert light energy into neural signals are called