Brilliant Pattern

1. Brilliant Pattern • Problem • Suspend a water drop at the lower end of a vertical pipe. Illuminate the drop using a laser pointer and observe the pattern created on a screen. Study and explain the structure of the pattern

2. Overview • Hypothesis • Assumption of Experiment • Experimental Setup • Devices and Process • Investigations • Experimental Results • Theory • The Physics Behind Brilliant Pattern • Conclusion

3. Hypothesis • Effects of reflection and refraction • Diffraction Geometrical Optics + Physical Optics d/2 a Physical Optics

4. 10 mw, 532 nm, Radius: 1.45 mm 1 mm Laser Pointer 35 cm Experimental Setup

5. Observation

6. Observation 42o 51o

7. Theory • Passing through water drop (0o)

9. Snell’s Law

10. Theory • Traveling backwards (180o)

12. Experimental Results 0o 42o 51o

13. Experimental Video

14. Experiment 2: Physical Optics • Distance between water drop and screen 4 m • Water Droplet Radius: 0.9~2 mm • Laser Pointer Diameter: 2.2 mm Wavelength: 532 nm

15. Experiment 2: Physical Optics Diffraction

16. Theory Huygens’s Principle Every point on a propagating wavefront serves as the source of spherical secondary wavelets, wavelets, such that the wavefront at some later time is the envelope of these wavelets

17. Theory • Huygens’s Principle • Every point on a propagating wavefront serves as the source of spherical secondary wavelets, wavelets, such that the wavefront at some later time is the envelope of these wavelets

18. BesselFunction a

20. Theoretical Analysis 0.9 mm Diameter of water drop: 1.2 mm 1.5 mm 2.0 mm

21. 0.9 mm 1.2 mm 1.5 mm 2 mm Theoretical Analysis Diameter of water drop:

22. 1.2 mm 0.9 mm 1.5 mm 2 mm Experimental Results Experimental Results 1.2 mm 0.9 mm 1.5 mm 2 mm

23. Experimental Results 0.9 mm 2 mm

24. Conclusion • Geometrical Optics: • At 0o the light passes through the water droplet and is magnified • The light is reflected and refracted by the water droplet; thus, interference is demonstrated • At other degrees because the light beam has attenuated its energy so patterns are unable to be observed • Wave Optics: • Due to Huygens’s principle, light is diffracted, so diffraction bands are observable • As water droplets are enlarged the distance between each band decreases

25. Thanks for your attention