Using ray diagrams to better understand everyday reality – Demo

One of the easiest way to visualize ray diagrams for lenses is by using an array of arrows on the board as the object and the camera on your phone as the screen.

(i) Convex Lens : Arrows on the board are placed outside the focal length of the lens -> Inverted image

Convex lens ray diagram visualization
Convex lens demo-outside the focal point

(ii) Convex Lens :Arrows on the board are placed inside the focal length of the lens -> Magnified Erect image

Convex lens demo- inside the focal point
Convex lens ray diagram visualization

(iii) Concave Lens: Irrespective of whether you place the arrows inside or outside the focal length, you get an erect image.

concave lens demo
concave lens ray diagram

(iv) Convex mirror: Virtually erect image formed from a Christmas ornament

The following video from UCLA extends the ray diagram analysis for concave and convex mirrors:

Physics of invisibility

(This page will be updated as the quarter progresses with other techniques that you will eventually learn about)

There are many way to make things “disappear” and impart the illusion of invisibility. Based on what you have studied so far, here is one possible ways you can do so. (There are certainly other ways and I strongly recommend spending some time thinking about this)

Using the refractive index


If you want to make something invisible,you have to ensure that the index of refraction of the object and the medium where you are hiding it remain the same and also that the object is transparent and colorless. 

The refractive index of a polymer ball is identical to that of water and if you immerse a colorless polymer ball in water, you can make it ‘disappear’ like the animation above shows you.

When you immerse colored polymer balls in water on the other, they seem as if they are 2-d objects although they are spheres!

Polymer balls and the physics of invisibility.
Colored Polymer balls appear as 2D circles when immersed in water