Presentation on theme: "Chapter 25. The Reflection of Light: Mirrors"— Presentation transcript:
1 Chapter 25. The Reflection of Light: Mirrors 25.1. Wave Fronts and Rays25.2. The Reflection of Light25.3. The Formation of Images by a Plane Mirror25.4. The Formation of Images by Spherical Mirror25.5. The Mirror Equation and Magnification Equation
2 A hemispherical view of a sound wave emitted by a pulsating sphere. 25.1 Wave Fronts and RaysA hemispherical view ofa sound wave emitted by apulsating sphere.Wave fronts: the surfaces through all points of the wave that are in the same phase of motion are called wave fronts.Rays: the radial lines pointing outward from the source and perpendicular to the wave fronts are called rays. The rays point in the direction of the velocity of the wave.
3 At large distances from the source, the wave fronts become less 25.1 Wave Fronts and RaysAt large distances from the source, the wave fronts become lessand less curved.Waves whose wave fronts are flat surfaces (i.e., planes) are known as plane waves.
4 The Reflection of Light Why are we able to see things around us?
5 25.2 The Reflection of Light LAW OF REFLECTIONThe incident ray, the reflected ray, and the normalto the surface all lie in the same plane, and the angleof incidence equals the angle of reflection.
6 25.2 The Reflection of Light In specular reflection, the reflected rays are parallel to eachother.
7 Example 1Two plane mirrors are separated by 120°, as the drawing illustrates. If a ray strikes mirror M1, at a 65° angle of incidence, at what angle q does it leave mirror M2?
8 25.3 The Formation of Images by a Plane Mirror The person’s right hand becomesthe image’s left hand.The image has three properties:It is upright.It is the same size as you are.The image is as far behind the mmirror are you are in front of it.
9 25.3 The Formation of Images by a Plane Mirror Why an image appears to originate from behind a plane mirror and upright?A ray of light from the top of the chess piece reflects from the mirror.To the eye, the ray seems to come from behind the mirror.Because none of the rays actually emanate from the image, it iscalled a virtual image.Real images are those from which all the light rays actually do emanate.
10 25.3 The Formation of Images by a Plane Mirror Why the image is located as far behind a plane mirror as the object is in front of it?The geometry used to show that the image distance is equalto the object distance.
11 25.3 The Formation of Images by a Plane Mirror Conceptual Example 1 Full-Length Versus Half-Length MirrorsWhat is the minimum mirror height necessary for her to see her fullimage?
12 25.3 The Formation of Images by a Plane Mirror Conceptual Example 2 Multiple ReflectionsA person is sitting in front of two mirrors that intersect at a right angle.The person sees three images of herself. Why are there three, ratherthan two, images?
13 Check Your Understanding The drawing shows a light ray undergoing multiple reflections from a mirrored corridor. The walls of the corridor are either parallel or perpendicular to one another. If the initial angle of incidence is 35°, what is the angle of reflection when the ray makes its last reflection?
14 mirror. If the outside surface is polished, is it a convex mirror. 25.4 Spherical MirrorsIf the inside surface of the spherical mirror is polished, it is a concavemirror. If the outside surface is polished, is it a convex mirror.The law of reflection applies, just as it does for a plane mirror.The principal axis of the mirror is a straight line drawn through thecenter and the midpoint of the mirror.
15 A point on the tree lies on the principal axis of the concave mirror. 25.4 Spherical MirrorsA point on the tree lies on the principal axis of the concave mirror.Rays from that point that are near the principal axis cross the axisat the image point.
16 Light rays near and parallel to the principal axis are reflected 25.4 Spherical MirrorsLight rays near and parallel to the principal axis are reflectedfrom the concave mirror and converge at the focal point.The focal length is the distance between the focal point andthe mirror.
17 The focal point of a concave mirror is halfway between 25.4 Spherical MirrorsThe focal point of a concave mirror is halfway betweenthe center of curvature of the mirror C and the mirror at B.
18 Rays that lie close to the principal axis are called paraxial rays. 25.4 Spherical MirrorsRays that lie close to the principal axis are called paraxial rays.Rays that are far from the principal axis do not converge to a singlepoint. The fact that a spherical mirror does not bring all parallelrays to a single point is known as spherical aberration.
20 When paraxial light rays that are parallel to the principal axis 25.4 Spherical MirrorsWhen paraxial light rays that are parallel to the principal axisstrike a convex mirror, the rays appear to originate from the focalpoint.
21 25.5 The Formation of Images by Spherical Mirrors CONCAVE MIRRORSThis ray is initially parallel to the principal axisand passes through the focal point.This ray initially passes through the focal point,then emerges parallel to the principal axis.This ray travels along a line that passes throughthe center.
22 25.5 The Formation of Images by Spherical Mirrors Image formation and the principle of reversibility
23 25.5 The Formation of Images by Spherical Mirrors When an object is located between the focal point and a concave mirror,and enlarged, upright, and virtual image is produced.
24 25.5 The Formation of Images by Spherical Mirrors CONVEX MIRRORSRay 1 is initially parallel to the principal axis and appears to originate fromthe focal point.Ray 2 heads towards the focal point, emerging parallel to the principal axis.Ray 3 travels toward the center of curvature and reflects back on itself.
25 25.5 The Formation of Images by Spherical Mirrors The virtual image is diminished in size and upright.
27 25.6 The Mirror Equation and Magnification Summary of Sign Conventions for Spherical Mirrors
28 25.6 The Mirror Equation and Magnification These diagrams are usedto derive the mirror equation.
29 25.6 The Mirror Equation and Magnification Example 5 A Virtual Image Formed by a Convex MirrorA convex mirror is used to reflect light from an object placed 66 cm infront of the mirror. The focal length of the mirror is -46 cm. Find the locationof the image and the magnification.