Reflection and Refraction

1. Chapter 29 Reflection and Refraction

2. Reflection • Reflection:when a wave reaches the boundary between two mediums, it bounces back into the first medium • based on rigidity • If second medium is very rigid – all energy is reflected • If second medium is less rigid – some energy is reflected, and some is transmitted

3. Reflection of Light • For light: • Metal surface is “very rigid” to light, so almost everything is reflected • Other substances, like glass and water, are “less rigid” so only a little bit is reflected

4. The Law of Reflection • Think of waves as straight line rays • The incident (before hitting boundary) ray • The reflected (after hitting boundary) ray • The incident ray and reflected ray make equal angles with a line perpendicular to the surface(Normal) • Angle of incidence • Angle of reflection

5. Mirrors • For a plane (flat) mirror • Creates a virtual image (the object appears to be behind the mirror where there is no actual light) • Image size = object size • Image distance = object distance • Image is reversed • There are also concave and convex mirrors that can make images bigger/smaller, closer/further, not reverse, etc…

6. Diffuse Reflection • When light hits a rough surface, each light ray is reflected differently • Some surface may be rough to some waves but flat (polished) to others • Usually based on wavelength or type of wave

7. Reflection of Sound • Called an echo • Sound reflects from all surfaces • Different for each material and shape • Study of how it does so is acoustics • When sounds reflect multiple times and interferes (reverberations) sound becomes garbled/ incoherent

8. Refraction • When a wave enters a new medium at an angle, it turns (one side of the wave slows down, while the other side does not) • Ocean waves: deep water to shallow water • Light: air to water/glass • To help understand this we draw wave fronts (lines that match up all crests for parallel waves)

9. Refraction of Sound • Sound Waves refract like all other waves • Ex: sound travels faster through warm air, slower in cold – sound bends away from the ground on a hot day • Ex: at night it is reversed – sound bends back towards the ground

10. Refraction of Light • As light passes from one medium to another it refracts • Prisms • “Bent” straws • Glass bottle/cups

11. Atmospheric Refraction • Mirages: • On hot days the air above the ground is hotter than higher up, so light refracts in layers, bending up • Brain reads the light as traveling in a straight line, so sees a “reflection” • Similarly, after the sun is “down” we still see it due to refraction

12. The Rainbow • Each raindrop acts like a tiny prism for the sunlight • Red (due to frequency) refracts 42 degrees • Violet refracts 40 degrees

13. Total Internal Reflection • At a certain angle (critical angle) the light no longer transmits into the medium at all (all reflects) • About 43 degrees for glass, 48 degrees for water • Prisms work better for this than mirrors • Creates fiber optics • Diamonds have lowest critical angle of any known substance (24.6 degrees)