Video Transcript
The diagram shows some apparatus
used in holography, including a cylindrical object. Which of the following is the
apparatus used for? (a) Viewing a recorded hologram of
an object. (b) Recording a hologram of an
object. (c) Both recording and viewing a
hologram of an object.
Okay, so taking a look at our
diagram, we see that it shows us this holographic apparatus. Our problem statement talks about a
cylindrical object. We can see that here. And along with this, we can
identify some other parts of this setup. For example, this element here
looks to be a light source, in particular, a laser. We can assume it’s a laser because
we know that this apparatus overall is used in holography and these applications
require a coherent light source, like a laser.
So these red-colored beams that we
see traveling around our apparatus must be beams of laser light. And we can see that, at this point
in the laser beam’s path, it’s split so that part of the beam moves on ahead and
then part is reflected downward. And then at these two locations in
our apparatus, it seems that these elements are mirrors that reflect the incoming
laser light. After it’s been reflected, the
light in this upper beam is then spread out and then encounters this cylindrical
object.
According to our diagram, this
light is then reflected off of the object and ultimately lands here. And at this location, at this
plate, we see that this light from our upper light beam meets the light from our
lower beam. What we see happening then is that
light coming from an object, and we call this light our object beam, is interfering
with a second beam of light called the reference. And this interference takes place
and is recorded on this plate.
This plate is typically called a
photographic plate. And it records the light incident
on it. And because in this case we have
two beams of light interfering when they reach the plate, that interference pattern
is what will be recorded. So then what our apparatus overall
is accomplishing is it’s mixing together two beams of light, one reflected from our
object and one a reference beam. In such a way that the differences
between these two beams are recorded.
Another way to describe this
process is to say that we’re encoding an image of our object, in this case our
cylindrical object. This information is recorded in our
plate, where it can then be retrieved later by decoding it using a similar light
source. When that happens, it’s possible to
view a three-dimensional image, a hologram, of our cylindrical object. But this process and this apparatus
is focused entirely on recording that holographic information. We’re not viewing a hologram. And therefore, considering our
three answer choices, we can eliminate option (a) as well as option (c), both of
which talk about viewing a hologram. The apparatus we’re seeing is used
only to record a hologram. And so we’ll choose answer option
(b). This apparatus is used to record a
hologram of an object.
