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Mirrors.pptx
- 1. Light, Reflection, & Mirrors
- 2. Facts about Light It is a form of Electromagnetic Energy It is a part of the Electromagnetic Spectrum and the only part we can really see
- 3. Facts about Light The speed of light, c, is constant in a vacuum. Light can be: REFLECTED ABSORBED REFRACTED Light is an electromagnetic wave in that it has wave like properties which can be influenced by electric and magnetic fields.
- 4. To study the reflection of light, we need a simple way to draw situations we are interested in. A convenient method is to use rays. A ray is an arrow that points in the direction that light travels.
- 5. The Reflection of Light The circles represent crests of the outgoing waves. The outward motion of the waves is indicated by the outward-pointing arrows the rays. Rays are always at right angles to the wave fronts. A similar situation applies to light and other electromagnetic waves, as illustrated in the figure below. 息 2014 Pearson Education, Inc.
- 11. A digital micromirror projection system is shown in the figure below.
- 13. Suppose, instead, that light travels from point A to a mirror, reflects from the mirror, and then continues to point B. This situation is shown in the figure below. Which path should the light take if it is to get to B in the least time? That is, from which point on the mirror should the light reflect?
- 14. This path is also the shortest possible reflecting path from A to B. The distances (and travel times) along paths 1 and 3 are greater, as is shown in the figure below.
- 17. An interesting application of mirror images is the heads- up display. An example from an airplane is shown in the figure below.
- 18. If three plane mirrors are joined at right angles, as shown in the figure below, the result is referred to as a corner reflector.
- 19. A typical spherical mirror is just a portion of a spherical shell of radius R.
- 20. The two situations are illustrated in the figures below.
- 22. Several parallel rays are shown approaching a convex mirror in the figure below.
- 30. Real Image Real Images are ones you can project on to a screen. For MIRRORS they always appear on the SAME SIDE of the mirror as the object. object image The characteristics of the image, however, may be different from the original object. These characteristics are: SIZE (reduced,enlarged,same size) POSITION (same side, opposite side) ORIENTATION (right side up, inverted) What if the mirror isnt flat?
- 31. Spherical Mirrors Concave & Convex Also called CONVERGING mirror Also called DIVERGING mirror
- 32. Converging (Concave) Mirror A converging mirror is one that is spherical in nature by which it can FOCUS parallel light rays to a point directly in front of its surface. Every spherical mirror can do this and this special point is at a fixed position for every mirror. We call this point the FOCAL POINT. To find this point you MUST use light from infinity Light from an infinite distance, most likely the sun.
- 33. Converging (Concave) Mirror Since the mirror is spherical it technically has a CENTER OF CURVATURE, C. The focal point happens to be HALF this distance. We also draw a line through the center of the mirror and call it the PRINCIPAL AXIS. f C C f 2 2
- 34. Ray Diagram A ray diagram is a pictorial representation of how the light travels to form an image and can tell you the characteristics of the image. Principal axis f C object Rule One: Draw a ray, starting from the top of the object, parallel to the principal axis and then through f after reflection.
- 35. Ray Diagrams Principal axis f C object Rule Two: Draw a ray, starting from the top of the object, through the focal point, then parallel to the principal axis after reflection.
- 36. Ray Diagrams Principal axis f C object Rule Three: Draw a ray, starting from the top of the object, through C, then back upon itself. What do you notice about the three lines? THEY INTERSECT The intersection is the location of the image.
- 37. Ray Diagram Image Characteristics Principal axis f C object After getting the intersection, draw an arrow down from the principal axis to the point of intersection. Then ask yourself these questions: 1) Is the image on the SAME or OPPOSITE side of the mirror as the object? Same, therefore it is a REAL IMAGE. 2) Is the image ENLARGED or REDUCED? 3) Is the image INVERTED or RIGHT SIDE UP?
- 38. Summary for Concave Mirror When object is: Beyond C At C Between C and F At F Between F and mirror Image is: Between C and F At C Beyond C No image Virtual image
- 39. The Mirror/Lens Equation Is there any OTHER way to predict image characteristics besides the ray diagram? YES! One way is to use the MIRROR/LENS equation to CALCULATE the position of the image. i o d d f 1 1 1
- 40. Mirror/Lens Equation Assume that a certain concave spherical mirror has a focal length of 10.0 cm. Locate the image for an object distance of 25 cm and describe the images characteristics. i i i o d d d d f 1 25 1 10 1 1 1 1 16.67 cm What does this tell us? First we know the image is BETWEEN C & f. Since the image distance is POSITIVE the image is a REAL IMAGE. Real image = positive image distance Virtual image = negative image distance What about the size and orientation?
- 41. Magnification Equation To calculate the orientation and size of the image we use the MAGNIFICATION EQUATION. x M M h h d d M o i o i 67 . 0 25 67 . 16 Here is how this works: If we get a POSITIVE magnification, the image is UPRIGHT. If we get a NEGATIVE magnification, the image is INVERTED If the magnification value is GREATER than 1, the image is ENLARGED. If the magnification value is LESS than 1, the image is REDUCED. If the magnification value is EQUAL to 1, the image is the SAME SIZE as the object. Using our previous data we see that our image was INVERTED, and REDUCED.
- 42. Example Assume that a certain concave spherical mirror has a focal length of 10.0 cm. Locate the image for an object distance of 5 cm and describe the images characteristics. 5 1 5 1 10 1 1 1 1 i i i i o d M d d d d f -10 cm 2x VIRTUAL (opposite side) Enlarged Upright Characteristics?