Video Transcript
Which of the following is a concave
lens? (A), (B), (C), (D), or (E)?
In this question, we are asked to
choose which picture shows a concave lens.
Let’s first think about what we
know about concave lenses. When viewed from the side, a
concave lens has this shape. The outline of a concave lens can
be drawn using a cylinder and two spheres viewed from the side. If we overlap these shapes like
this, we can see the shape of the concave lens. The lens is thinner in the middle
and thicker at the edges, with two curved sides.
To answer this question, we need to
decide which option is a concave lens. We can automatically discard shapes
(B) and (D). These are thicker in the middle and
thinner at the edges, so these cannot be convex lenses.
Similarly, we can rule out option
(D). Option (D) is thicker on the right
side than in the middle, and thinner on the left side than in the middle. This is not the shape of a concave
lens.
Now let’s look at option (A). This shape is thicker at the edges
than in the middle. But the edges are straight, not
curved, so this is not right.
We are left with option (C). We can see that it is thinner in
the middle than at the edges and that these edges are curved. This can also be drawn using a side
view of two spheres, like we described earlier. So this is a concave lens. The correct answer is option
(C).
