Please choose the correct ending to complete the given sentence: Education and Communications: [header] How to calculate the refractive index in physics [title] Measure the width of the transparent object. [step] 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. [title] Send light from a point light source through the object.

Ending1: [step] Light from an invisible window is visible through a transparent window. [title] Calculate refractive index by finding the refractive index number (pi). Ending2: [step] Monochromatic point light sources are available through laboratory supply outlets. Place the point light source a known distance from the surface of the object. Ending3: [step] Suppose a window pane has a thickness of 180 degrees. However, as a general rule of thumb, you must send light that's smaller than 180 degrees through the object. Ending4: [step] To generate a refractive index, plug light into a fraction of their length and have the light propagate from the fraction to the center point. A chart, for example, would use a point light source, to represent the diameter of a space.

Answer format: ending1/ending2/ending3/ending4