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Reflection of Light

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Definitions

  • Luminous objects – generate their own light (the sun)

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  • Illuminated objects – reflect light (the moon)

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  • Line of Sight – a line from an object or image to your eyes (light from the object travels along this line to your eyes)

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Line of Sight

  • Both luminous & illuminated objects emit/reflect light in many directions.
  • Your eye sees only the very small diverging cone of rays that is coming toward it.

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Slide 3

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Rays of Light

  • Incident Ray – leaves the object and strikes the mirror

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  • Reflected Ray – leaves mirror and strikes your eye

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  • The reflected ray is on the line of sight from the image to your eye.

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Law of Reflection

  • Angle of incidence equals angle of reflection.

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Law of Reflection

  • Normal – line perpendicular to the mirror surface

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  • Angle of incidence – angle between incident ray and normal

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  • Angle of reflection – angle between reflected ray and normal

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Slide 6

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Law of Reflection Animation

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θi = θr

Slide 7

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Diffuse Reflection

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Diffuse Reflection

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Wet Road Glare

  • Driving at night on a wet roadway results in an annoying glare from oncoming headlights.

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Observing an Image

  • An image is a position in space from which all reflected light appears to diverge.

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  • Image formed by a plane mirror is called a virtual image.

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  • Virtual images are formed in regions where there is actually no light

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Image Location

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Image Formed By Plane Mirror

  • Image is virtual.

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  • Image is located as far behind the mirror as the object is in front of the mirror.

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How Big Must the Mirror Be?

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Distance from Mirror Irrelevant

Slide 15

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Right Angle Mirror

Slide 16

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Right Angle Mirror

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  • Formation of primary and secondary images

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Kaleidoscope

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  • Angles smaller than 90o produce more than 3 images

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Kaleidoscope Applets

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Slide 19

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Reflection Applets

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Law of Reflection�Curved Mirrors

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  • Angle of Incidence is equal to the angle of reflection

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Converging Mirror

  • A series of flat mirrors can be arranged to reflect parallel light through a single point.

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  • Increasing the number of flat mirrors causes the shape to more closely approximate a parabola and causes the reflected light to converge in a smaller area.

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Parabolic vs Spherical

  • Close to the axis of the mirror, the parabola and the circle are almost the same shape.
  • Farther from axis the parabola flattens out.
  • It is easier and less expensive to make spherical mirrors.

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Types of Curved Mirrors

  • A concave mirror is silvered on the inside of the sphere.
  • A concave mirror is also called a converging mirror because it converges parallel light.
  • A convex mirror is silvered on the outside of the bowl.
  • A convex mirror is also called a diverging mirror because it diverges parallel light.

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Concave Mirror Terms

  • Axis
  • Center of Curvature
  • Radius of Curvature
  • Focus
  • Focal Length

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Three Useful Rays

  • Ray parallel to the axis reflects through the focus.
  • Ray through the focus reflects parallel to the axis.
  • Ray through the center of curvature reflects back on itself.