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Chapter 26 Optics I (Mirrors)

Chapter 26 Optics I (Mirrors). Laser. LIGHT. Properties of light: Light travels in straight lines:. Light travels VERY FAST How fast?. At this speed it can go around the world 8 times in one second. Can you think of an example to prove that light travels much faster than sound? .

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Chapter 26 Optics I (Mirrors)

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  1. Chapter 26Optics I (Mirrors)

  2. Laser LIGHT • Propertiesof light: • Light travels in straight lines:

  3. Light travels VERYFAST • How fast? At this speed it can go around the world 8 times in one second. Can you think of an example to prove that light travels much faster than sound?

  4. Luminous and non-luminous objects A luminous object is one that produces light. A non-luminous object is one that reflects light. Luminousobjects Reflectors • The Moon • Mirrors • People • Objects -The Sun - Lamps - Lights - Lasers - Campfires

  5. Reflection of light If the surface off which the light is reflected is smooth, then the light undergoes specular reflection (parallel rays will all be reflected in the same directions). If, on the other hand, the surface is rough, then the light will undergo diffuse reflection (parallel rays will be reflected in a variety of directions)

  6. The Law of Reflection For specular reflection the incident angle qi equals the reflected angle qr: qi=qr The angles are measured relative to the normal, shown here as a dotted line.

  7. di do hi ho Forming Images with a Plane Mirror do = distance from object to mirror di = distance from image to mirror ho = height of object hi= height of image For a plane mirror: do = -diand ho = hi

  8. di do ho hi Plane Mirrors A plane mirror image has the following properties: • The image distance equals the object distance ( in magnitude ) • The image is unmagnified • The image is virtual (what is virtual?): • negative image distance • di < 0 • m>0, The image is not inverted

  9. Spherical Mirrors concave A spherical mirror is a mirror whose surface shape is spherical with radius of curvature R. There are two types of spherical mirrors: concave and convex. We will always orient the mirrors so that the reflecting surface is on the left. The object will be on the left. convex

  10. Focal Point When parallel rays (e.g. rays from a distance source) are incident upon a spherical mirror, the reflected rays intersect at the focal point F, a distance R/2 from the mirror. (Locally, the mirror is a flat surface, perpendicular to the radius drawn from C, at an angle q from the axis of symmetry of the mirror). For a concave mirror, the focal point is in front of the mirror (real). For a convex mirror, the focal point is behind the mirror (virtual). The incident rays diverge from the convex mirror, but they trace back to a virtual focal point F.

  11. A Focal Length The focal lengthf is the distance from the surface of the mirror to the focal point. M The focal length is half the radius of curvature of a spherical mirror. Sign Convention: the focal length is negative if the focal point is behind the mirror. For a concave mirror, f = ½R For a convex mirror, f = ½R (R is always positive)

  12. The Mirror Equation Sign Conventions: do is positive if the object is in front of the mirror (real object) do is negative if the object is in back of the mirror (virtual object) diis positive if the image is in front of the mirror (real image) di is negative if the image is behind the mirror (virtual image) f is positive for concave mirrors f is negative for convex mirrors m is positive for upright images m is negative for inverted images The ray tracing technique shows qualitatively where the image will be located. The distance from the mirror to the image, di, can be found from the mirror equation: do = distance from object to mirror di= distance from image to mirror f = focal length m = magnification

  13. Example 1 An object is placed 30 cm in front of a concave mirror of radius 10 cm. Where is the image located? Is it real or virtual? Is it upright or inverted? What is the magnification of the image?

  14. Spherical Mirrors – Concave Object Outside the Focal Point • Image is REAL, INVERTED, and DEMAGNIFIED !!! F C

  15. Example 2 An object is placed 6 cm in front of a concave mirror of radius 20 cm. Where is the image located? Is it real or virtual? Is it upright or inverted? What is the magnification of the image?

  16. Example 2 (continued)

  17. Spherical Mirrors – ConcaveObject Inside the Focal Point • Image is VIRTUAL, UPRIGHT, and MAGNIFIED F C C

  18. Example 3 An object is placed 5 cm in front of a convex mirror of focal length 10 cm. Where is the image located? Is it real or virtual? Is it upright or inverted? What is the magnification of the image?

  19. Example 3 (continued)

  20. Spherical Mirrors - Convex • Image is VIRTUAL, UPRIGHT, and DEMAGNIFIED C C F F

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