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Line of Sight
Line of sight - it is a simple idea, but a very powerful idea once you get a grasp of it. To see anything, you must sight at the thing. To see an image, you must sight at the image. When you sight at the thing - whether the image or some other object - light from the thing travels along a line to your eye. Your eye and the thing you are looking at are two points on the line of sight along that you are looking.
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Light travels in a straight line - that is the underlying principle of the line of sight idea (see Know the Law section above). One of the four diagrams can obviously be ruled out because of the curved path. Light reflects off a mirror; it doesn't pass through it. This allows you to rule out a second diagram. Finally, light follows the law of reflection (see Know the Law section below). This allows you to rule out a third diagram. There's one diagram left.
The final diagram (the right answer) should depict a person looking along a line at an image and light reflecting off the mirror along the line of sight. The light should be reflecting according to the law of reflection.
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The Law of Reflection:
When a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflection. The incident ray and reflected ray are always located within the same plane.
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