2TWO KIND OF REFLECTIONS The reflection of light can be roughly categorized into two types of reflection: specular reflection is defined as light reflected from a smooth surface at a definite angle, and diffuse reflection, which is produced by rough surfaces that tend to reflect light in all directions
3TWO KIND OF REFLECTIONS Specular reflectionDiffuse reflection
4When the diffuse reflection occur? It is hard to belive, but you have to know that all objects reflect rays, but those which surface is not flat give diffuse reflection and become indirect-lighting device. Yes, your hand also reflects and diffuse much of the light it receives. Its surface is rough, so rays have different angles of incidence and different angles of reflection and are diffused. This phenomenon allows us to see objects which are not the sources of light.
5FLAT MIRRORA virtual image is produced by a flat mirror because of specular reflectionHow the mirror build a virtual image?
6How the mirror work?The incident and reflected rays all lie in a plane that includes the normal (dashed line).
7How the mirror work?hh’Images are classified as real or virtual. A real image is formed when light rays pass through and diverge from the image point; a virtual image is formed when the light rays do not pass through the image point but appear to diverge from that point.Lateral magnification
8How the mirror work?A flat mirror produces an image that has an apparent left–right reversal. You can see this reversal by standing in front of a mirror and raising your right hand. The image you see raises its left hand. Likewise, your hair appears to be parted on the side opposite your real part, and a mole on your right cheek appears to be on your left cheek.
9Quick Quiz!!In the overhead view, the image of the stone seen by observer 1 is at C. Where does observer 2 see the image—at A, at B, at C, at D, at E, or not at all?
10The Fermat PrincipleThe time required for light to travel from point A to B is the minimum time required For propagation in the same medium, the velocity is a constant and this minimizing the time is the same as minimizing the distance traveled.
11The Fermat Principlei = Three possible paths from A to B are shown. Let's look at the arbitrary path ACB. If point A' is constructed on the perpendicular AO such that AO = A'O, the right triangles AOC and A'OC are equal. Thus AC = A'C and the distance traveled by the ray of light from A to B via C is the same distance from A' to B via C. The shortest distance from A' to B is obviously the straight line A'DB, so the path ADB is the correct choice taken by the actual light ray.
12Spherical MirrorA spherical mirror, as its name implies, has the shape of a section of a sphere.This type of mirror focuses incoming parallel rays to a point, as demonstrated bythe colored light rays.
13Concave MirrorThe incoming rays from the object are essentially parallel because the source is assumed to be very far from the mirror. We call the image point in this special case the focal point F and the image distance the focal length f = R/2
14Concave Mirror(a) A concave mirror of radius R. The center of curvature C is located on theprincipal axis. (b) A point object placed at O in front of a concave sphericalmirror of radius R, where O is any point on the principal axis farther than Rfrom the mirror surface, forms a real image at I. If the rays diverge from O atsmall angles, they all re.ect through the same image point.
16Concave Mirror Lateral magnification : Mirror equation : In term of f :
17Concave MirrorWhen the object is located so that the center of curvature lies betweenthe object and a concave mirror surface, the image is real, inverted, and reduced in size.
18Concave MirrorWhen the object is located between the focal point and a concave mirror surface, the image is virtual, upright, and enlarged.
19Convex MirrorWhen the object is in front of a convex mirror, the image isvirtual, upright, and reduced in size.
20How to describe an image ? Assume that a certain spherical mirror has a focal length of cm.Locate and describe the image for object distances of (a) 25.0 cm,(b) 10.0 cm, and (c) 5.00 cm.We find the image distance by using mirror equation:Because q is positive, the image is realThe magnification is given byBecause M is negative, the image is invertedThe image is real, inverted, and reduced in size.Because of less than 1, the image is reduce in sizeLook at the figure
21Index of RefractionThe index of refraction (n) is defined as the speed of light (c) in vacuum divided by the speed of light in the medium (vp).Speed of light, c = m/sc = km/s
22Index of Refraction Material Index, n Vacuum 1.00000 Air 1.0008 Water 1.330Glass1.510Diamond2.417Ruby1.760Ice1.30What is the speed of light inside a diamond?What is the speed of light inside water?
23Snell’s LawSnell's Law relates the indices of refraction n of the two media to the directions of propagation in terms of the angles to the normal.
26Critical AngleWhen light passes through a medium of high refractive index into a medium of lower refractive index, the incident angle of the light waves becomes an important factor. If the incident angle increases past a specific value, it will reach a point where the angle is so large that no light is refracted into the medium of lower refractive index. The four yellow light rays all have an angle of incidence (i) low enough to pass through the interface between the two media. However, the two red light rays have incident angles that exceed the critical angle (approximately 41 degrees) and are reflected either into the boundary between the media or back into the high refractive index medium.
27Critical Angle / Total Reflection The following picture shows the total reflection of light inside the glass block. The light enters the glass block from the lower right and travels in a zigzag way inside the glass block by total reflection.