This is a test of commonsense. Complete the next sentence:

How to calculate the refractive index in physics
Measure the width of the transparent object.
For example, a pane of window glass has a thickness that may be stated by the manufacturer, but which should be measured to ensure accurate calculation of the refractive index.
Send light from a point light source through the object.
Monochromatic point light sources are available through laboratory supply outlets. Place the point light source a known distance from the surface of the object.