Question Video: Identifying the Pattern Produced from a Holographic Recording Focused by a Convex Lens | Nagwa Question Video: Identifying the Pattern Produced from a Holographic Recording Focused by a Convex Lens | Nagwa

# Question Video: Identifying the Pattern Produced from a Holographic Recording Focused by a Convex Lens Physics • Third Year of Secondary School

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Which of the following would be observed if the object beam of a holographic recording was focused by a convex lens and projected onto a screen? [A] A three-dimensional real image of the object. [B] An interference pattern. [C] A two-dimensional real image of the object. [D] A patch of uniform-intensity light.

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### Video Transcript

Which of the following would be observed if the object beam of a holographic recording was focused by a convex lens and projected onto a screen? (A) A three-dimensional real image of the object. (B) An interference pattern. (C) A two-dimensional real image of the object. (D) A patch of uniform-intensity light.

Here is an apparatus used for recording a holographic image of this orange cylinder. Along with the beam splitter, here, and the two plane mirrors, here and here, there are also lenses used in this setup. These are concave lenses that diverge parallel light rays. These lenses have the opposite effect to convex lenses that converge parallel light rays at a focus.

Let’s look more closely at the beam of light going from the object being imaged to the holographic plate, called the object beam. We can see that the rays of this beam are diverging and do not focus at a point. If a convex lens with the required focal length was placed in the path of the object beam, the rays in the object beam would focus at its focal point. The rays on the opposite side of the focal point would then form a real image if they were incident on a screen. We see then that if an object beam is focused with a convex lens and projected on a screen, the result would be a real image. Two answer options refer to a real image. But one of the options states that the real image would be three-dimensional and the other that the real image would be two-dimensional.

Holographic recording produces three-dimensional images. So it might seem that the image produced on a screen by focusing an object beam would be three-dimensional. In this case though, that is not the right answer. The three-dimensional properties of holographic recorded images depend on interference between the object beam and another beam of light called the reference beam. The question only refers to an object beam and does not say that the object beam interacts with a reference beam. Also, holographic images are not viewable as they are recorded, only afterward when a playback beam is used to illuminate the recorded image.

Considering only an object beam projected onto a screen, what would be produced would be a two-dimensional real image. So the correct answer is option (C).

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