Basics

General Description

A mirror may seem complicated but actually it’s not! All it consists of is a pane of glass that has a special reflective coating on one side of it.  The coating is what reflects the light back off of the mirror and into your eye.

Law of Reflection

When light hits a plane (flat) mirror it is reflected according to the law of reflection. This law says that “the angle of incidence is equal to the angle of reflection.”  This means that the incoming angle is always equal to the angle leaving the surface. Have you ever wondered why the sun’s glare during the evening and morning is so much more intense than during the rest of the day? Well, this can be explained using the Law of Reflection.  The light from the sun hits the Earth’s surface at a very low angle and it comes off the Earth at the same low angle.  This means that the sun’s light hits your eyes more directly at these times.

    

Image Point

When you look at an object in a mirror, you see a virtual image of that object in the mirror.  Virtual images are images that are formed in locations where light does not actually reach. The light does not actually pass through to the other side of the mirror but to the observer it appears to do so. How is this virtual image formed and what is its location? As light waves hit a mirror they reflect by the law of reflection. If you were to take all the reflected light rays and extend them back behind the mirror, they would all intersect at a certain point.  That point is the location of the virtual image that you see when you look into the mirror- the image point.  It doesn’t matter at which angle you look into the mirror, the object will have the same image point.

         

Specular Reflection

When you look at your Chapel Hill t-shirt in the mirror, you may notice that the words Tar Heels don’t look quite right, they look flipped or backwards. Although we may want to think that mirrors switch things left to right or right to left, that is actually not the case.  It actually acts as a printing press or a rubber stamp; it switches things front to back.  The reflection you see in the mirror is a light print (stamp print) of you.

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