Video: Who Can See Who?

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Who Can See Who?

Video Transcript
Suppose you have five students sitting in front of a plane mirror … and an Observer, marked O on the diagram. How can we predict which students the Observer sees in the mirror?

The first step to answering this question is to locate the images of each student. Measure from student A to the mirror and directly across the mirror the same distance. Mark the image of student A. Label it as A'. The prime symbol (') indicates image. Repeat the procedure for all students.

Now in order to see anything, you must sight along a line at that thing. For instance, to see the Monkey up there in the corner, I must sight directly in line with the Monkey. When I do, light from the Monkey comes along my line of sight to my eye. And to see the image of an object in a mirror, I must sight at the image. And when I do, light from the object will reflect off the mirror and travel along the line of sight to my eye.

The second step is to align a sight line from the Observer to each student’s image. If the sight line intersects the mirror, then the Observer can see that student’s image in the mirror. For Student A: the line of sight to A’s image intersects the mirror; so light from Student A reflects off the mirror to the Observer’s eye. But when the Observer sights at Student B’s image, there is no mirror along that line of sight to reflect light to the Observer’s eye. This Observer can see Student A in the mirror but not Student B. Repeat this line of sight method for all students. And you will find that this Observer can see Students A, C, and D in the mirror but not B and E.

I’m Mr. H, letting you know that … You got this!


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