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Question Video: Determining the Purpose of Some Holography Apparatus Physics

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

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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.

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