Question Video: Know That Plane Mirrors Produce an Image of Equal Size to the Object Science

Light from an object is reflected by a plane mirror. The mirror produces an image of the object. Which of the following correctly describes how the sizes of the object and its image compare? [A] The image is larger than the object. [B] The image is smaller than the object. [C] The image is the same size as the object.

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Video Transcript

Light from an object is reflected by a plane mirror. The mirror produces an image of the object. Which of the following correctly describes how the sizes of the object and its image compare? (A) The image is larger than the object. (B) The image is smaller than the object. (C) The image is the same size as the object.

To see which answer is correct, imagine we look at a plane mirror from the side. Since the mirror is plane, from this perspective, it will look like a straight line. If an object is put in front of the mirror and an observer looks at the mirror, then that observer will see light from the object that is bounced off the mirror. By tracing those reflected light rays backward, the observer can see an image of the object. Our question is, is that image larger, smaller, or the same size as the object? Since we have here a plane mirror, that is, a flat mirror, it will always reflect light so that the size of the image matches the size of the object. That is, the image and the object have the same size. If our mirror was not a plane mirror, it might reflect light so that the image is not the same size as the object. But because it is plane, they are the same size.

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