Experiment 14

Experiment 14

REFLECTION and REFRACTION

of LIGHT

PROCEDURE

Set up the apparatus as shown in Fig. 14-2, and turn on the light source. The room should be dark enough that the light rays on the Ray Table are visible. Carry out the following procedures.

1. Open up the R&R Workbook and fill in the header information. Record the answers to the questions found at the end of each step on the Worksheet.

Figure 14-2: Apparatus for Light Ray Observation

Straight Line Propagation of Light:

2. Observe the light rays on the Ray Table, and answer Questions 1 and 2 on the Worksheet.

3. Rotate the Slit Plate slowly on the component holder until the slits are horizontal. Observe the slit images on the Viewing Screen and answer Questions 3 through 5 on the Worksheet.

Locating the Bulb Filament:

4. Refer to the diagram in Fig. 14-3. Place a piece of blank white paper on top of the Ray Table, and make a reference mark on the paper at the position of the center of the Ray Table. Using a pencil and a straight edge, trace the edges of several of the rays onto the paper.

Figure 14-3: Ray Tracing

5. Remove the paper. Use the pencil and straight edge to extend each of the rays back to the source. Trace them back to their common point of intersection. You may need to tape on an additional sheet of paper. Label the filament location and the center of the Ray Table on your diagram.

6. Use the scale on the Optics Bench to measure the distance between the filament and the center of the Ray Table directly. Record the distance in cell F49.

Law of Reflection:

7. Use the set up shown in Fig. 14-4, with the Slit Mask in place and the Ray Optics Mirror mounted on the Ray Table. Adjust the components so that a single ray of light is aligned with the boldface arrow labeled "NORMAL" on the Ray Table Degree Scale. Carefully align the reflecting surface of the mirror with the boldface line labeled "COMPONENT" on the Ray Table. With the mirror properly aligned, the boldface arrow on the Ray Table is normal (perpendicular) to the plane of the reflecting surface.

Figure 14-4: Law of Reflection Set Up

8. Rotate the Ray Table and observe the incident and reflected light rays. The angles of incidence and of reflection are measured with respect to the normal to the reflecting surface, as shown in Fig. 14-5.

Figure 14-5: Ray Table Set Up for Reflection

The plane that contains the incident ray and the normal to the mirror is called the plane of incidence. In this experiment, the plane of incidence is the top surface of the Ray Table.

9. By rotating the Ray Table, set the angle of incidence to successive settings of: 0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80° and 90°. For each angle of incidence, record the angle of reflection in cells D55:D64 of the Data Table on the Worksheet. Answer Question 6 on the Worksheet.

Figure 14-6: Determination of Image Location

Image Formation in a Plane Mirror:

10. Use the set up as before with the Slit Plate alone in the holder (no Slit Mask). Adjust the Slit Plate and the Light Source positions for sharp, easily visible rays. As shown, place a blank white sheet of paper on top of the Ray Table, and place the Ray Optics Mirror on top of the paper. Position the mirror so that all of the light rays are reflected from its flat surface. Draw a line on the paper to mark the position of the flat surface of the mirror.

11. Look into the mirror along the line of the reflected rays so that you can see the image of the Slit Plate and, through the slits, the filament of the Light Source. Answer Question 7 on the Worksheet.

12. With a pencil, mark two points along one edge of each of the incident and reflected rays. Label the points r₁, r₂, etc., so that you know which points belong to which ray.

13. Remove the paper and reconstruct the rays as shown in Fig. 14-6, using a pencil and straight edge. If you need to, tape on additional pieces of paper. Draw dotted lines to extend the incident and reflected rays. On your drawing, label the position of the filament d₁ and the apparent position of its reflected image d₂.

14. Change the position of the mirror and repeat the measurements for a different orientation of the mirror.

Law of Refraction:

15. Set up the equipment as shown in Fig. 14-7, using the Slit Mask and the Cylindrical Lens on the Ray Table. Adjust the components so that a single ray of light passes directly through the center of the Ray Table Degree Scale. Align the flat surface of the Cylindrical Lens with the line labeled "COMPONENT". With the lens properly aligned, the radial lines that extend from the center of the Degree Scale will all be perpendicular to the circular surface of the lens itself. The angle measurement is illustrated in Fig. 14-8.

Figure 14-7: Law of Refraction Set Up

16. Without disturbing the alignment of the lens, rotate the Ray Table and observe the refracted ray for various angles of incidence. By rotating the Ray Table, set the angle of incidence θ_i to: 0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, and 90°. For each angle of incidence θ_i, measure and record the angle of refraction θ_r in cells D87:D96 on the Worksheet.

Figure 14-8: Ray Table Set Up for Refraction

17. Obtain a print out of your Worksheet and use it to develop your lab report.