Half-round slabs of glass or plastic are often used to trace rays. Pins are placed at points P and Q. For an observer to see the images of the pins in line, she should place her eye at point

Question

Quizplus · Accepted Answer

The observer should place her eye at point 3, which is the point where the line passing through the pins and the normal to the surface at point R intersect. This is because the angle of incidence equals the angle of reflection, and the normal to the surface at point R bisects the angle between the incident and reflected rays. So, the reflected ray from pin P will pass through point R and be directed towards point 3, and the reflected ray from pin Q will also pass through point R and be directed towards point 3, where the observer's eye should be placed to see the images of the pins in line.

Half-Round Slabs of Glass or Plastic Are Often Used to Trace