Video Transcript
Which of the following materials
could a concave lens be made of? (A) Wood, (B) glass, (C) copper,
(D) steel, (E) concrete.
Let’s first remember that a lens is
a piece of transparent material with a particular shape that can be used to change
the direction that light rays are traveling in. A transparent material is one that
allows light to pass through it. In other words, it is
see-through. So the material we are looking for
must be see-through and let rays of light pass through it.
To answer this question, we can
look at the options we have been given and decide which of these materials are
transparent. We know that wood is not
transparent. We wouldn’t expect to be able to
see through a tree, for example. So (A) cannot be the correct
answer. Similarly, metals like copper or
steel aren’t transparent. We wouldn’t expect to be able to
see through a copper coin or a steel saucepan. So neither option (C) nor option
(D) can be correct. Concrete is also not
transparent. We know that we can’t see through
concrete walls, for example. So (E) cannot be the correct
answer.
Glass, however, is transparent. We know that light can pass through
things like glass windows, which are used to let sunlight into buildings and allow
us to see outside. So glass is the only transparent
material in this list. All the other materials are opaque,
which means they don’t let light travel through them. Glass is the only material on the
list that we could make a concave lens out of, or any other lens for that
matter. So the correct answer then is
option (B), glass.
