We now know what images are: apparent reproductions of objects. In the last chap
We now know what images are: apparent reproductions of objects. In the last chapter, we characterized images as and , and discussed the idea of . Our next goal is to determine where these images will be for a given optical system. To solve this, we will use a new type of problem solving called ray tracing. Ray tracing is a type of problem solving quite different than what you are used to for physics classes; this method of problem solving uses a lot more diagrams and, while equations will still be used, they will play a comparatively smaller role. These multiple problem solving approaches goes back to Physics Goal #2: Representing physics Ideas in different ways.
So what is ray tracing? If an object emits light, it emits light in all directions. If the object is visible by reflecting light from another source, your face is visible because it reflects light from the surroundings, that reflected light is diffuse and goes in all directions. Also keep in mind, that typical objects emit huge (1030) numbers of photons. Thus, there are effectively photons going in every conceivable direction as shown in Figure 1.
Ray tracing allows us to follow very specific photons: photons which will easy to follow because of the paths they take. For example, we know from the last chapter, that a photon that enters a converging lens parallel to the optical axis will go through the focal point as shown in Figure 2 below. Since there are so many photons, leaving your face, one will go parallel to the optical axis and then through the lens and towards the focal point as shown in Figure 1.
Throughout the next few sections, we will go through the particular rays to follow for the different :
For each optical element, there will be three rays to follow for any object a finite distance away (if the object is infinitely far away, then the rays come in parallel and we saw what happens with parallel rays in the previous chapter). The three rays to follow are:
Our three rays that we will follow
A ray that comes in parallel to the optical axis leaves using a focal point. If the optical element is (like a concave mirror or convex lens) then use a focal point that brings the ray towards the optical axis.
A ray that aims for the center of a lens or mirror will go straight.
The center of a lens is the middle: this ray will travel un-deflected as though the lens was not there.
The center of a mirror is the geometric center: this ray will hit the mirror at a 90o angle and bounce straight back.
A ray that comes in using a focal point will exit parallel to the optical axis.
Instructor’s Note
Your quiz will cover:
For a given ray, you need to be able to determine where it will go for each of these basic optical elements
We will NOT expect you to be able to interpret the results, do calculations, or consider multiple elements. We will do that in class.
Ray Tracing for Converging Lenses
Instructor’s Note
All of the following sections are presented both as video and with a text-based transcr