Section 2 Flat Mirrors. Distinguish between specular and diffuse reflection of light. Apply the law of reflection for flat mirrors.

Transcription

1 Section 2 Flat Mirrors Objectives Distinguish between specular and diffuse reflection of light. Apply the law of reflection for flat mirrors. Describe the nature of images formed by flat mirrors.

2 Section 2 Flat Mirrors Reflection of Light Reflection is the change in direction of an electromagnetic wave at a surface that causes it (a wave) to move away from the surface. The texture of a surface affects how it reflects light. Diffuse reflection is reflection from a rough, texture surface such as paper or unpolished wood. Specular reflection is reflection from a smooth, shiny surface such as a mirror or a water surface.

3 Section 2 Flat Mirrors Reflection of Light, continued The angle of incidence is the the angle between a ray that strikes a surface and the line perpendicular to that surface at the point of contact. The angle of reflection is the angle formed by the line perpendicular to a surface and the direction in which a reflected ray moves. The angle of incidence = the angle of reflection

4 Section 2 Flat Mirrors Angle of Incidence and Angle of Reflection

5 Section 2 Flat Mirrors Flat Mirrors Flat mirrors form virtual images that are the same distance from the mirror s surface as the object is. The image formed by rays that appear to come from the image point behind the mirror but never really do is called a virtual image. A virtual image can never be displayed on a physical surface.

6 Section 2 Flat Mirrors Image Formation by a Flat Mirror

7 Section 2 Flat Mirrors Comparing Real and Virtual Images

8 Objectives Calculate distances and focal lengths using the mirror equation for concave and convex spherical mirrors. Draw ray diagrams to find the image distance and magnification for concave and convex spherical mirrors. Distinguish between real and virtual images. Describe how parabolic mirrors differ from spherical mirrors.

9 Concave Spherical Mirrors A concave spherical mirror is a mirror whose reflecting surface is a segment of the inside of a sphere. Concave mirrors can be used to form real images. A real image is an image formed when rays of light actually pass through a point on the image. Real images can be projected onto a screen.

10 Image Formation by a Concave Spherical Mirror

11 Concave Spherical Mirrors, continued The Mirror Equation relates object distance (p), image distance (q), and focal length (f) of a spherical mirror. 1 p + 1 q = 1 f 1 object distance + 1 image distance = 1 focal length

12 Concave Spherical Mirrors, continued The Equation for Magnification relates image height or distance to object height or distance, respectively. h' q M = = h p image height magnification = = object height image distance object distance

13 Rules for Drawing Reference Rays for Mirrors

14 Concave Spherical Mirrors, continued Ray diagrams can be used for checking values calculated from the mirror and magnification equations for concave spherical mirrors. Concave mirrors can produce both real and virtual images.

15 Ray Tracing for a Concave Spherical Mirror

16 Sample Problem Imaging with Concave Mirrors A concave spherical mirror has a focal length of 10.0 cm. Locate the image of a pencil that is placed upright 30.0 cm from the mirror. Find the magnification of the image. Draw a ray diagram to confirm your answer.

17 Sample Problem, continued Imaging with Concave Mirrors 1. Determine the sign and magnitude of the focal length and object size. f = cm p = cm The mirror is concave, so f is positive. The object is in front of the mirror, so p is positive.

18 Sample Problem, continued Imaging with Concave Mirrors 2. Draw a ray diagram using the rules for drawing reference rays.

19 Sample Problem, continued Imaging with Concave Mirrors 3. Use the mirror equation to relate the object and image distances to the focal length. 1 p + 1 q = 1 f 4. Use the magnification equation in terms of object and image distances. M = q p

20 Sample Problem, continued 5. Rearrange the equation to isolate the image distance, and calculate. Subtract the reciprocal of the object distance from the reciprocal of the focal length to obtain an expression for the unknown image distance. = q f p

21 Sample Problem, continued Substitute the values for f and p into the mirror equation and the magnification equation to find the image distance and magnification = = = q 10.0 cm 30.0 cm cm cm cm q = 15 cm M q 15 cm = = = 0.50 p 30.0 cm

22 Sample Problem, continued 6. Evaluate your answer in terms of the image location and size. The image appears between the focal point (10.0 cm) and the center of curvature (20.0 cm), as confirmed by the ray diagram. The image is smaller than the object and inverted ( 1 < M < 0), as is also confirmed by the ray diagram. The image is therefore real.

23 Convex Spherical Mirrors A convex spherical mirror is a mirror whose reflecting surface is outward-curved segment of a sphere. Light rays diverge upon reflection from a convex mirror, forming a virtual image that is always smaller than the object.

24 Image Formation by a Convex Spherical Mirror

25 Sample Problem Convex Mirrors An upright pencil is placed in front of a convex spherical mirror with a focal length of 8.00 cm. An erect image 2.50 cm tall is formed 4.44 cm behind the mirror. Find the position of the object, the magnification of the image, and the height of the pencil.

26 Sample Problem, continued Convex Mirrors Given: Because the mirror is convex, the focal length is negative. The image is behind the mirror, so q is also negative. f = 8.00 cm q = 4.44 cm h = 2.50 cm Unknown: p =? h =?

27 Sample Problem, continued Convex Mirrors Diagram:

28 Sample Problem, continued Convex Mirrors 2. Plan Choose an equation or situation: Use the mirror equation and the magnification formula h' q + = and M = = p q f h p Rearrange the equation to isolate the unknown: p = and h = h' p f q q

29 Sample Problem, continued Convex Mirrors 3. Calculate Substitute the values into the equation and solve: = p 8.00 cm 4.44 cm = = p cm cm cm p = 10.0 cm

30 Sample Problem, continued Convex Mirrors 3. Calculate, continued Substitute the values for p and q to find the magnification of the image. q 4.44 cm M = = M = p 10.0 cm Substitute the values for p, q, and h to find the height of the object. p 10.0 cm h = h' = (2.50 cm) q 4.44 cm h = 5.63 cm

31 Ray Tracing for a Convex Spherical Mirror

32 Parabolic Mirrors Images created by spherical mirrors suffer from spherical aberration. Spherical aberration occurs when parallel rays far from the principal axis converge away from the mirrors focal point. Parabolic mirrors eliminate spherical aberration. All parallel rays converge at the focal point of a parabolic mirror.

33 Spherical Aberration and Parabolic Mirrors

34 Reflecting Telescope

35 Section 4 Color and Polarization Objectives Recognize how additive colors affect the color of light. Recognize how pigments affect the color of reflected light. Explain how linearly polarized light is formed and detected.

36 Section 4 Color and Polarization Color Additive primary colors produce white light when combined. Light of different colors can be produced by adding light consisting of the primary additive colors (red, green, and blue).

37 Section 4 Color and Polarization Additive Color Mixing

38 Section 4 Color and Polarization Color, continued Subtractive primary colors filter out all light when combined. Pigments can be produced by combining subtractive colors (magenta, yellow, and cyan).

39 Section 4 Color and Polarization Subtractive Color Mixing

40 Section 4 Color and Polarization Polarization of Light Waves Linear polarization is the alignment of electromagnetic waves in such a way that the vibrations of the electric fields in each of the waves are parallel to each other. Light can be linearly polarized through transmission. The line along which light is polarized is called the transmission axis of that substance.

41 Section 4 Color and Polarization Linearly Polarized Light

42 Section 4 Color and Polarization Aligned and Crossed Polarizing Filters Aligned Filters Crossed Filters

43 Section 4 Color and Polarization Polarization of Light Waves Light can be polarized by reflection and scattering. At a particular angle, reflected light is polarized horizontally. The sunlight scattered by air molecules is polarized for an observer on Earth s surface.

44 Section 4 Color and Polarization Polarization by Reflection and Scattering