# Reflection Light incident upon a boundary between

## Presentation on theme: "Reflection Light incident upon a boundary between"— Presentation transcript:

29.1 - Reflection Light incident upon a boundary between
two medium causes a portion of the light to return back to original medium – reflection All wave energy returned – totally reflected Some energy reflected some transmitted – partially reflected Metals are almost totally reflective – why so shiny Water and glass reflect a much smaller amount (2% & 4%)

29.2 – The Law of Reflection Light rays reflect at the same angle as they are incident Angle of incidence = angle of reflection These angles are measured to the perpendicular of the surface – called the normal

29.3 - Mirrors An infinite number of light rays leave the candle
Each obeys the law of reflection Only some reflect back to your eye These appear to come from behind the mirror There is no light behind the mirror – a virtual image is produced Flat mirrors only produce virtual images

Your eye cannot tell the difference between real and virtual images
Light enters the eye the same way For flat (plane) mirrors, the image appears the same distance behind mirror as object is in front The image and object are the same size

29.4 – Diffuse Reflection If a surface has imperfections about the size of one wavelength or larger – light “sees” it as rough The reflections produced are in many different directions, that is, diffuse reflection If wavelength larger than imperfections, the surface is considered smooth (specular reflection) Therefore, reflections can only be seen at particular angles – equal to angle of incidence

9.4 ½ - Curved Mirrors Shaped like sections of a sphere
May be reflective on inside (concave - converging) or outside (convex - diverging)

29.4 ½ - Curved Mirrors Parallel rays incident on a concave mirror reflect at common point called focal point (F) The distance between focal point and mirrored surface – focal length (f) The center of sphere that produced mirror curve, center of curvature, C = 2 f

To generate a ray diagram – three rays are used, all begin on the object
A parallel ray is reflected through focal point A ray through the focal point is reflected parallel A ray perpendicular to mirror reflects back on itself (goes through the center of curvature)

29.4 ½ - CONT. There are three descriptors for the image produced
Real or virtual (or none) Upright or inverted Larger or smaller (or same size)

29.4 ½ - CONCAVE - CONVERGING
Object outside the center of curvature (2 f) – image is real, inverted & smaller

29.4 ½ - CONCAVE - CONVERGING
Object inside focal point – image is virtual, upright and larger

29.4 ½ - CONVEX - DIVERGENT For convex mirrors, the rays diverge after reflecting off mirror Since they never meet in “front” of mirror, they never form real images We backtrace imaginary rays behind mirror

29.4 ½ - CONVEX - DIVERGENT For a convex mirror – image is always virtual, upright & smaller

29.4 ½ - MIRROR SIGN CONVENTION
CONCAVE f is positive Image can be real or virtual Real image is always inverted can be larger or smaller Virtual image is always upright and larger CONVEX f is negative Image is always virtual Image is always upright and smaller