Video Transcript
Which of the following is a concave
lens? (A), (B), (C), or (D)?
This question is asking us to
identify a concave lens. Let’s first remember that a concave
lens is made up of a transparent material that lets light travel through it. When viewed from the side, a
concave lens has this shape.
To understand this shape, we can
think about viewing a cylinder and two spheres from the side, like this. Now let’s move the shapes closer
together so that the two spheres overlap the cylinder. The shape of the concave lens is
what we would get if we were to cut away from the cylinder the area where the two
spheres overlap it. The most important thing to
remember is that a concave lens is thinner in the middle than at its edges and that
it has two curved surfaces.
Now let’s look at the options we
have been given and see if we can identify the concave lens. All of these objects appear to be
made of the same material, but they have different shapes. Let’s start with options (A) and
(B). Both of these are thicker in the
middle than they are at the edges, so these are not concave lenses. Plus, option (A) does not appear to
have any curved surfaces. So, these cannot be correct
answers.
Option (C) is also not correct. Although its bottom edge is thicker
than its middle, its top edge is very thin. And it doesn’t appear to have any
curved surfaces. So, this is not concave. Looking at option (D), we can see
that it is thinner in the center than at the edges, and the edges are also
curved. This is a concave lens. So, option (D) is the correct
answer.
