Oscillations and Waves Wave Properties

1. Oscillations and WavesWave Properties

2. 4.5 Wave properties 4.5.1 Describe the reflection and transmission of waves at a boundary between two media. 4.5.2 State and apply Snell’s law.. 4.5.3 Explain and discuss qualitatively the diffraction of waves at apertures and obstacles. 4.5.4 Describe examples of diffraction. 4.5.5 State the principle of superposition and explain what is meant by constructive interference and by destructive interference. 4.5.6 State and apply the conditions for constructive and for destructive interference in terms of path difference and phase difference. 4.5.7 Apply the principle of superposition to determine the resultant of two waves.

3. Consider the following images. What do you notice about the behaviour of light in the different media? http://www.3d-digital-graphic-art.com/page-op-art-refraction-tutorial.html http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/optpic/brokpen.jpg

4. In the previous slide you would have noticed images created by light changing direction or bending. The bending of light is called REFRACTION. As light passes from one medium to another, the speed of light changes. This causes to light to be “bent” or refracted.

5. When a light ray passes into a medium in which it travels slower (a more optically dense medium) it is refracted towards the normal. When a light ray passes into a medium in which it travels faster (a less optically dense medium) it is refracted away from the normal.

6. http://micro.magnet.fsu.edu/optics/lightandcolor/refraction.htmlhttp://micro.magnet.fsu.edu/optics/lightandcolor/refraction.html http://micro.magnet.fsu.edu/primer/java/refraction/refractionangles/index.html In 1621, Dutch physicist, Willebrord Snell studied refraction carefully and discovered a mathematical relationship between the angles of incidence and refraction.

7. That relationship, known as Snell’s law, is http://sol.sci.uop.edu/~jfalward/refraction/refraction.html The constant is known as the RELATIVE REFRACTIVE INDEX. Another way to write Snell’s Law is where n1 is the refractive index of the incident substance and n2 is the refractive index of the refractive substance.

10. As an angle of incidence increases, the intensity of the reflected beam increases and less light is transmitted. This continues until, at a certain angle of incidence called the critical angle, the angle of refraction will be almost 90° and the transmitted ray travels just along the surface. If the angle of incidence is then increased beyond the critical angle no ray is transmitted and total internal reflection will occur.

11. What is the critical angle for water given that the refractive index for water is 1.3?

12. Refraction helps to explain Apparent Depth. The apparent depth of a body of water on the right appears less than its actual depth. Light rays from a point of the bottom of the pool are refracted at the water’s surface. Coin demo

13. Refraction also helps to explain Mirages. Mirages occur because the different temperature gradients in the atmosphere act like boundary layers and refract the light coming from the sky. The image of “water” that you see in the distance is actually just a refraction of the sky above. http://www.unmuseum.mus.pa.us/mirage.htm http://www.islandnet.com/~see/weather/elements/mirage1.htm http://mintaka.sdsu.edu/GF/explain/simulations/inf-mir/Kaplan_photos.html

14. Diffraction

17. Superposition

18. A Standing Wave – same frequency and amplitude A Beat Wave – slightly different frequency

21. Path Difference For constructive interference, For destructive interference,

23. Dr Quantum - Double Slit Experiment

24. Physics - Single Slit Diffraction 1 of 2 (from http://www.youtube.com/watch?v=A-q8_4UbmpI)

25. Physics - Single Slit Diffraction 2 of 2 (from http://www.youtube.com/watch?v=tsgVqLgUrc4)