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Reflection Ch. 17

Reflection Ch. 17. GPS Standards:. Students will analyze the properties and applications of waves. Explain the processes that result in the production and energy transfer of electromagnetic waves.

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Reflection Ch. 17

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  1. Reflection Ch. 17

  2. GPS Standards: Students will analyze the properties and applications of waves. • Explain the processes that result in the production and energy transfer of electromagnetic waves. • Experimentally determine the behavior of waves in various media in terms of reflection, refraction, and diffraction of waves. • Explain the relationship between the phenomena of interference and the principle of superposition. • Demonstrate the transfer of energy through different mediums by mechanical waves. • Determine the location and nature of images formed by the reflection or refraction of light.

  3. Reflection • a wave reaches a boundary and it bounces back into the first media as it strikes that boundary. It may be: • Total - all of the wave’s energy reflects back. Ex: light hitting aluminum, chrome, other metals • Partial – some of the wave’s energy reflects back. Ex: light waves hitting water of glass

  4. Law of Reflection • Waves bounce back at the same angle at which they arrived. Direction of waves are shown using straight line rays. Incident and reflected rays make equal angles perpendicular to a surface called the normal • Angle of incidence = Angle of Reflection

  5. Diffuse Reflection • Light is reflected in many directions from a rough surface. • Rough surface varies depending on the type of wave which comes in contact with it. What may seem like a rough surface to one type of wave may seem like a polished surface to another type.

  6. Diffuse Reflection (cont.) • Most things around us are seen by diffuse reflection, such as the light which reflects from a book you read, because the surface of ordinary paper as seen through a microscope in is actually quite rough! • To see a beam of light shined on a piece of paper, your eye can be at any position, but to see a beam of light reflected from a small mirror, your eye must be at just the right place.

  7. Mirrors 3 main types: • Plane (flat mirror like in the bathroom) • Concave (inwardly curved make-up/shaving mirrors) • Convex (outwardly curved car/grocery store mirrors)

  8. Diverging Light • An object is a source of diverging light rays. The object can send out its own light rays (like a light bulb) or can reflect light.

  9. How Parallel Light Rays Reflect: • When parallel light rays are incident on a mirror, they can reflect with 3 possible options: • Remain parallel (only happens with a plane mirror) • Converge (all rays eventually meet at a single point) happens with a concave mirror • Diverge (all rays spread away from each other) happens with a convex mirror

  10. Which way is which?

  11. Plane Mirror • Objects seen appear to be somewhere behind mirror. Eye sees the reflected light and extrapolates its path back to a point behind the mirror where it appears to originate. • What you see is called a VIRTUAL IMAGE. • Plane mirrors cannot produce a REAL IMAGE because parallel light rays that strike the mirror always reflect parallel to each other. • Reflected light rays must intersect in order to form a REAL IMAGE.

  12. In Plane Mirrors: • object size = the image size • object distance in front of the mirror = image distance behind the mirror.

  13. Concave Mirrors • When parallel light rays hit a concave mirror, mirror’s curvature causes them to be reflected non-parallel to each other. • If object is placed beyond the focal point of concave mirror, all light rays from a single point on object intersect at a single point upon reflection. • Light rays converging on a single point in real space will produce a REAL IMAGE because the light rays appear to be radiating from that point as they continue onward.

  14. Concave Mirrors also… • can create a VIRTUAL IMAGE: If object is placed closer to mirror than focal point, reflected light rays diverge. Observer would see a virtual image located somewhere behind the mirror because the light appears to originate from that point. • can create NO IMAGE at all when an object is placed exactly at the focal point, the reflected light rays run parallel to each other. Ex: Instead, would see a wide beam of parallel light like that of flashlight or car headlights

  15. Concave Mirrors cont. • Virtual images formed by concave mirrors are larger and farther away from the mirror than the object is. • http://hyperphysics.phy-astr.gsu.edu/Hbase/geoopt/mirray.html

  16. Convex vs. Concave Mirrors

  17. Convex Mirrors • Virtual images formed by convex mirrors are smaller and closer to the mirror than the object is. • http://hyperphysics.phy-astr.gsu.edu/Hbase/geoopt/mirray.html

  18. Spherical Aberration • Special Note: • Parallel light rays that are far from the principal axis are not reflected by spherical mirrors to converge at the focal point. This defect is called spherical aberration. To avoid this dilemma, spherical mirrors have been replaced with parabolic mirrors in devices such as telescopes that require extreme accuracy and focus.

  19. Lens/Mirror Equation • (units of length MUST match) • f stands for focal length • di is the distance from the mirror/lens to the image • do is the distance from the mirror/lens to the object

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