Video Transcript
The diagram shows a laser being
used to record a holographic image of a cylindrical object and then to display the
image recorded on the holographic plate. Which of the virtual images shown
would be observed by a viewer at the position shown? (A) Virtual image A. (B) Virtual image B. (C) Both virtual images
simultaneously. (D) Each virtual image would
alternate. (E) Neither virtual image.
In the top half of our diagram, we
see laser light being split into two different beams where one of these beams
interacts with our object of interest and the other provides a reference for that
object beam. When these two beams interfere at
our holographic plate, a hologram of our cylindrical object is formed. In order to actually see this
hologram though, the holographic plate where the hologram is recorded needs to be
exposed to the same light that was used to record the hologram in the first
place. When that happens, an image of the
hologram can become visible.
In the bottom half of our diagram,
there are two candidate virtual images: virtual image A here and virtual image B
here. We want to know which one, or
perhaps both, or perhaps neither will this observing eye see. If we look back at how our hologram
was recorded, we see that the holographic plate is located here, and relative to
that our object is here. We might think then that since
virtual image A is located in roughly the same position as our original object
relative to our holographic plate, that this would be the image that would form and
be observed by the eye. A key here, though, is that the
observing eye must look on a line of sight through the holographic plate in order to
see any image that’s formed. We can trace this line of sight as
far as we like, and we see that no image is formed along it.
Because of the position of the
observing eye relative to the holographic plate, the eye is unable to see either
virtual image A or virtual image B. A line of sight from the eye
through the holographic plate passes through neither one of those images. So, for our answer, we choose
option (E). Of the two virtual images shown
here, the observing eye sees neither virtual image because neither one is along the
eye’s line of sight.
