6.1 Reflection

6.1.1 Angles of Incidence and Reflection

1. Position the incandescent light source on the left end of the optical bench and place the angular translator about 25 cm from the end of the light source housing. Make sure the 0 mark lies on a line parallel to the bench. Adjust the rotating table so that the scored lines run perpendicular and parallel to the bench.
2. Attach the aperture mask to the standard component carrier and place it between the light source and angular translator so the the mask is d centimeters from the center of the translator. The distance d (about 6.5 cm) is the measured distance from the center of the angular translator to the first analyzer holder on the movable arc. (See Fig. 6.1.2.)
3. Center the viewing screen of the special component carrier designed for use with the angular translator, and place the assembly on the rotating table of the translator so that the front surface of the viewing screen coincides with the scored line on the table which runs perpendicular to the optical bench.
4. Now switch on the light and adjust the aperture mask's position (don't move the component carrier) until the entire image is on the viewing screen. With the aid of the millimeter scale marked on the screen, center the image horizontally. Turn the screen 90 and center the image vertically.
5. Replace the viewing screen with the flat surface mirror (be careful not to touch the front surface of the mirror) such that the mirror surface coincides with the perpendicularly scored line. Move the viewing screen to the first analyzer holder on the movable arc.
6. Rotate the table a set number of degrees (for example 30 ), and then move the arm until the reflected image is centered horizontally on the viewing screen. Record the angle which the arm makes with the mirror. Repeat for several settings of the rotating table. What is the relation between the angle of incidence and the angle of reflection? Both of these angles are measured from the ray to the normal of the reflecting surface.
7. Rotate the viewing screen and measure the vertical position of the reflected image. Compare this with the vertical position of the incident beam (from your initial alignment of the laser beam). Check that the incident ray, reflected ray and normal to the mirror at the point of reflection all lie in the same plane.

6.1.2 Reflections from Glass and Acrylic

1. Replace the flat mirror with the glass plate, taking care that the front surface coincides with the scored line.
2. Rotate the table until the glass plate rests at a convenient angle with the optical bench.
3. Move the arm until the reflected image is visible on the viewing screen. How many images of the beam are there? Why?
4. The brightest image is the reflection from the front surface of the glass. Center this image on the screen and record the angle which the translator arm makes with the glass plate. Repeat the procedure with the rotating table set at several different angles. What is the relation between the angle of incidence and the angle of reflection?
5. Measure the height of the middle of the reflected image; determine whether the incident ray, reflected ray and normal to the glass at the point of reflection are coplanar.
6. Replace the glass plate with the acrylic plate and repeat the above procedure. Does the material used as the reflecting surface affect the relationship between the angles of incidence and reflection?

  

Figure 6.1.2: Experimental Setup.