2.3 : Reflection and Refraction

1. 2.3: Reflection and Refraction 7.6.c Students know light travels in straight lines if the medium it travels through does not change. 7.6.g Students know the angle of reflection of a light beam is equal to the angel of incidence

2. Reflection When an object or wave hits a surface through which it cannot pass, it bounces back. Angle of incidence- Angle between the incoming wave and the normal Angle of reflection- angle between the reflected wave and the normal Key concept: The law of reflection states that the angle of incidence equals the angle of reflection.

3. Light travels in straight lines unless the medium it is traveling through changes • When light hits a shiny surface it bounces back

4. Mirrors • Image- copy of an object formed by reflected or refracted rays of light • Optical axis- an imaginary line that divides a mirror in half • Focal point- point where rays parallel to the optical axis meet or converge

5. Mirrors: Plane Mirrors • Plane mirror- flat sheet of glass that has a smooth, silver-colored coating on the one side • Image appears to be as far behind the mirror as the object is in front of the mirror • The reflected light from an object looks as through it came from a point behind the mirror • Creates a virtual image that is upright and same size- but not quite the same

6. Mirrors • Virtual image- upright image that forms where light seems to come from (image appears behind mirror) • Real image- forms when rays actually meet Real Virtual

7. Mirrors: Concave Mirrors A mirror with a surface that curves inward like the inside of a bowl is a concave mirror. Reflects rays that are parallel back through the focal point

8. Mirrors: Concave Mirrors Concave mirrors can form either virtual images or real images.

9. Mirrors: Concave Mirrors • The location of the focal point depends on the shape of the mirrors • Concave mirrors can either be can be either virtual or real • Virtual images formed by a concave mirror are always larger than the image

10. Mirrors: Convex Mirrors • Object in mirror are closer than they appear • Can never create a real image because the rays never meet • Disadvantage: image is reduced in size- appears to be further away than it is • Advantage: allows you to see a larger area than you can with a plane mirror • Where they are used: security, passenger side mirrors, safety mirrors in banks, parking garages, offices

11. Mirrors: Convex Mirrors A mirror with a surface that curves outward is called a convex mirror.

12. Refraction Key Concept: When light rays enter a medium at an angle, the change in speed causes the rays to bend, or change direction. Light travels in straight lines if the medium does not change If light enters a new medium it might slow down or speed up

13. Refraction • Different densities in the same medium cause refraction • Stars twinkle because of variations in the density in the Earth’s atmosphere • Rainbows are a pretty effect caused by refraction- it is the separation of the visible light • The longer the wavelength the less the wave is bent by a prism

14. Lenses • Lens- a curved piece of glass or other transparent material that refracts light • A lens forms an image by refracting light rays passing through it • The type of image formed depends on the shape of the lens and the position of the object • Focal length- the distance from the lens to the focal point

15. Lenses: Convex Key Concept: An object’s position relative to the focal point determines whether a convex lens forms a real image or a virtual image. ` Convex lens- thicker in the center than the edge

16. Lenses: Concave Key concept: A concave lens can produce only virtual images because parallel light rays passing through the lens never meet. Concave lens- thinner in the center than the edges