Question Video: Observing Images Produced by Plane Mirrors Science

An object is located in front of a plane mirror. Light from the object is reflected by the plane mirror that produces an image of the object. Which of the following correctly describes where the image appears to be? [A] Behind the mirror [B] In front of the mirror [C] At the position of the mirror

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Video Transcript

An object is located in front of a plane mirror. Light from the object is reflected by the plane mirror that produces an image of the object. Which of the following correctly describes where the image appears to be? (A) Behind the mirror, (B) in front of the mirror, or (C) at the position of the mirror.

This question asks about the image of an object produced by a plane mirror. If you were to look into a plane mirror directly in front of you, you’d see what appears to be yourself. But what you actually see is light reflected from the mirror. Some of the light that reflects off the mirror first came from you, and your eye sees this light as your reflection.

Now, in this situation, we could say that you are the object. That is, your body is a physical thing that occupies a volume of space. The thing in the mirror that appears to be you then is an image of the object. Now, the image is not an object. It doesn’t occupy a volume of space. It’s an effect produced by light rays reflecting from the surface of the mirror.

So it might seem that the image is at the position of the mirror. After all, it’s the mirror that produces an image. However, the question doesn’t ask where the image is or where it’s produced. It asks where the image appears to be. When considering the apparent properties of an image, it’s really important that we remember that, to our eyes and brain, light always appears to travel in an uninterrupted straight line. Let’s bear this in mind as we consider what really happens when a plane mirror reflects light rays and produces an image.

So let’s imagine we have an object, in this case a flower, positioned in front of a plane mirror. Light from the environment reflects off the object in all directions. And some of this light reflects off the mirror and into the eye of an observer. Now, remember that our eyes and brains are only able to interpret light as if it traveled in a straight line. This means that the observer’s eye will see this light as if it has traveled in a straight path, along the dotted line shown.

So the light from the object appears to have come from here, behind the mirror. This means that the object appears to be located behind the mirror. This is what forms the image. And this is why it appears to be located behind the mirror, even though in fact an image doesn’t really have a location at all. The correct answer then is option (A). The image of the object appears to be behind the mirror.

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