The Physics
Opus in profectus


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  1. When light strikes glass perpendicularly about 4% is reflected at each surface. How much light is transmitted through a pane of window glass?
  2. Why can't auto focus cameras be used to photograph themselves in a mirror? Why will the auto focusing mechanism cause the camera to take a blurry picture of its image in a mirror?
  3. Why is the lettering on the front of some vehicles backward? Why is the lettering on the back and sides of these vehicles not also backward?
  4. Does the law of reflection hold for curved mirrors? Does it hold for diffuse reflection? Does it hold when light is scattered off nitrogen molecules in the Earth's atmosphere?
  5. What minimum height must a "full length" mirror have so that when you look into it you are able to see your entire body. Draw a diagram to illustrate the way it works. (Hint, Hint, Hint: Draw the diagram first. Draw a profile view of a stick figure standing in front of a wall. Draw a ray from the foot of the stick figure that bounces off the wall and travels to the eye of the stick figure. Draw a ray from the top of the stick figure's head that bounces off the wall and travels to the stick figure's eye. That's enough of a hint. You should be able to answer the question now.)


  1. caroms.pdf
    The diagram below shows two mirrors that meet at a right angle. Several rays of light enter from above and strike the mirror on the left. Draw the path of one ray as it reflects first off the left mirror and then off the lower mirror.

    2 plane mirrors at a right angle. 9 rays of light incident at various angles upon a point on one of them.

    1. What numbered point does the ray pass through as it leaves the diagram?
    2. How does the direction of the ray entering the diagram compare to the direction of the ray that left the diagram?
  2. The diagram below shows a semicircular mirror with 12 incident rays of light. The letter "C" marks the center of the semicircle and the dashed line is the axis of the mirror. All 12 incident rays are parallel to the axis. Draw the reflected rays until they reach the axis. Do they focus?

    Cross-section of a hemispherical mirror and 12 parallel incident rays coming in from the left