Law of Reflection

Law of Reflection

• Ref p329 Copy Figure 1 into notebook and label all vocabulary terms
  • vocabulary
    • incident ray - note direction of ray (from a light source)
    • reflected ray
    • point of incidence
    • normal - (dashed line)
    • angle of incidence - (always measured from normal, why would this be a good convention?)
    • angle of reflection - (always measured from normal, why would this be a good convention?), note small r, (capitol R is reserved for Refraction)
  • Notes - Law of Reflection
    • <i=<r
    • incident ray, reflected ray and normal are coplanar

Images in a Plane Mirror

• vocabulary
  • object point
  • virtual image point -
    • point from which the rays of light from an object appear to diverge
    • image is not real (there is no actual light where you perceive the image to be, if we put a sheet of paper at the image location there would be no image projected on it)
• Analysis of an image in a plane mirror, Two Methods

  	Method 1	Method 2
  Example	Text Book p330 Fig 3 - Reproduce this diagram in your notes	Downloadable handout - Reflected Images in Plane Mirrors to view see note 1
  Object	Consider the object as a single point.	The object is often depicted as an arrow. In the analysis the top of the arrow and the bottom of the arrow usually each analyzed.
  Eye	The eye is depicted larger than a single point and often in a larger than realistic scale. consider one ray going into the top of the iris and one ray going into the bottom of the iris in the analysis.	Consider the eye as a single point.
  Method	Consider two incident rays emanating from an object and striking a plane mirror. Draw both reflected rays such that they behave in accordance with the law of reflection. Project the reflected rays back behind the mirror surface using dashed lines. Where the virtual rays converge is the location of the virtual image.	Generate an incident ray from the top of the arrow and another from the bottom of the arrow, both reflect in accordance with the law of reflection in such a way that the reflected rays converge at the eye. Project back virtual rays behind the mirror surface with dotted lines. Use do=di and the location of the virtual rays locate the virtual image. Draw the virtual image in dashed lines. note 2 - solutions to the handout
  What this Demonstrates	This shows that di=do, and the image is virtual.	This shows ho=hi (height of object = height of image, no magnification of image), image is oriented upright (it is not inverted) and image is virtual

Characteristics of Images

• Magnification
  • Magnification is the ratio of the height of the image (hi) to the height of the object (ho).
• Orientation (Attitude)
  • The orientation may be upright or inverted
• Image Type
  • The image may be real or virtual.

   

• For a plane mirror, the image is upright, no magnification (hi=ho), and virtual. Also do=di.

Retroreflector and Illusions

• Define retroreflector and draw the ray diagram to explain the images on the handout sheet.