was then used to determine the wavelength of the light. This equation will be explained in more detail in the procedure section. In this equation \(d\) will be the distance between the marks on your ruler, namely one millimeter, and n will be a specified bright spot in the interference pattern. We will see later that the brightest spot will be specified as \(\left(n=0\right)\). Then \(\alpha\) will be the original incidence angle with the reflective ruler which is also \(\beta_0\), \(\beta\)n in general will be the angle from the ruler to every bright spot on the wall.
Procedure
First we will need to set up the reflective ruler in such a way that it is as close to perpendicular with the wall as can be managed. The laser will then be incident with the ruler at a small enough angle that the interference pattern will be present on the wall. It will be necessary to allow a small portion of your laser to pass the end of the ruler without reflecting so that we have a reference point to generate the lengths necessary to produce the angles \(\alpha\) and \(\beta_n\). Remember that the laser will also need to illuminate the ruler within the metric marks so that we have multiple places the laser will reflect from or we will not get a clean interference pattern, as well the original angle of incidence will need to be something on the order of 3 degrees or less or a pattern will not be created. Best results will occur if all equipment is maintained in the same plane relative to the floor. Your set up should look something like this.