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10.2

10.2. Properties of Light and Reflection. Reflection. Reflection. Reflection - the change in direction of a light ray when it bounces off a surface. Rays of Light. Light travels in a straight line (as long as it’s moving through the same medium)

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10.2

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  1. 10.2 Properties of Light and Reflection

  2. Reflection

  3. Reflection • Reflection - the change in direction of a light ray when it bounces off a surface

  4. Rays of Light • Light travels in a straight line (as long as it’s moving through the same medium) • Medium – the substance through which light travels • Ray-a straight line with an arrowhead that shows the direction in which light waves are travelling. • Ray diagrams - can be used to make predictions about appearance of objects

  5. Ray Model of Light • Ray – A single unit of light • Represented by 1 arrow • Beam – A bundle of light rays travelling in one direction • Represented by many arrows

  6. Definitions You Need to Know • incident ray – a ray of light that travels from a light source towards a surface • angle of incidence – angle between the incident ray and the normal in a ray diagram • normal - a line that is perpendicular to a surface where a ray of light meets the surface • reflected ray – a ray that begins at the point where the incident ray and the normal meet • angle of reflection – the angle between the reflected ray and the normal in a ray diagram • plane mirror – a mirror with a flat reflective surface

  7. Laws of Reflection • The incident ray, the reflected ray, and the normal always lie on the same plane. • 2. The angle of reflection is equal to the angle of incidence. • Law of reflection states that the angle of incidence equals the angle of reflection r = i

  8. Drawing Ray Diagrams Normal – dotted line perpendicular to the surface (90◦ angle)

  9. Ray Diagrams

  10. Protractor • http://www.amblesideprimary.com/ambleweb/mentalmaths/protractor.html • LET’S PRACTICE USING A PROTRACTOR

  11. Images in Plane Mirrors • Plane Mirror – A mirror with a flat, reflective surface • Scientists call an object in front of a mirror the object, and they call what is seen in the mirror the imageof the object. • Using the laws of reflection to rays going from the object, you can predict where the image will be and where the image would look like.

  12. Virtual Image • Virtual Image- an image formed by rays that appear to be coming from a certain position, but are not actually coming from this position • image does not form a visible projection on a screen • brain assumes that a light ray travels in a straight line • note the lateral inversionall images in plane mirrors are reversed

  13. Let’s use the power of Reflection on Abraham Lincoln’s face 

  14. Abraham Lincoln Left side face

  15. Abraham Lincoln “Left side” face “Right side” face

  16. Four Characteristics of an Image L.O.S.T 1. Location • closer than, farther than, or the same distance as the object to the mirror 2. Orientation • upright or inverted 3. Size • same size, larger than, or smaller than the object 4. Type • real or virtual image

  17. Characteristics of an Image in a Plane Mirror • 1. Location • the same distance as the object to the mirror • 2. Orientation • upright • 3. Size • same size • 4. Type • virtual image • You can predict these characteristics by drawing a ray diagram

  18. Location • Image is located on the same side of the mirror • Image is located on the opposite side of the mirror • Image can also be located at a specific point (e.g. at centre of curvature, f<di<2f, etc.) • Note: image location will always be di=do for plane mirrors

  19. Orientation a) Upright- image is right-side up b) Inverted- image is upside-down c) Laterally Inverted- image is flipped horizontally a) MIRROR b) MIRROR MIRROR c) MIRROR

  20. Size a) Enlarged - image is larger than the object b) Reduced - image is smaller than the object c) Same - image is the same size as the object a) b) c)

  21. Type • Real - image appears in front of the mirror (could be projected onto a screen) • Virtual - image appears behind the mirror

  22. Locating an Image in a Plane Mirror Using a Ray DiagramPage 416

  23. Locating an Image in a Plane Mirror Using a Ray Diagram

  24. Locating an Image in a Plane Mirror Using a Ray Diagram

  25. Locating an Image in a Plane Mirror Using a Ray Diagram

  26. Locating an Image in a Plane Mirror Using a Ray Diagram

  27. Reflection and Stealth Technology The shape of and surface paint on the stealth aircraft absorbs and reflects radar waves so that only a few of the waves reach the ground radar station. This renders the aircraft virtually invisible.

  28.  Homework  • Read Section 10.2 on Pages 411-416 • Complete # 1-4, 6 found on Page 418.

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