One type of mirror, known as a convex mirror, has a reflective surface that curves outward.
A convex mirror has a point where all the light that hits it appears to focus. This is called the focal point or sometimes simply the focus. The distance from the front of the mirror to the focal point is the focal length.
How can we tell what kind of image will be formed by a convex mirror? One way is to construct a ray diagram, which is simply a picture that shows the paths of a few important light rays as they hit the surface of the mirror and bounce back.
To make a ray diagram, first, draw the mirror in the middle of the page and then draw a horizontal axis right through the center of the mirror. Carefully measure the focal length, and mark this on the diagram. For a convex mirror, the focus will be behind the mirror. Now, measure the distance to the object and mark this distance in front of the mirror. You don't have to worry about drawing the object accurately. Just draw an upright arrow to represent the object.
Next, make the following three special rays. The first ray should be parallel to the horizontal axis and should go from the top of the object to the surface of the mirror. After it hits the mirror, it will be reflected back along a path lined up with the focal point.
The second ray will also begin at the object and will go towards the mirror along a path that is lined up with the focal point. When it hits the surface of the mirror, it will be reflected back parallel to the horizontal axis.
Finally, the third ray will extend from the top of the object to the center of the mirror. It will reflect back at the same angle that it hits the mirror.
Once you have these three rays, you can use them to find out where the image will be formed and the characteristics of the image (real or virtual, upright or inverted, bigger or smaller).
If the three rays you just drew all meet at a point in front of the mirror, then you have a real image. If they don't meet, you need to continue the three reflected lines back behind the mirror until they do meet. It's a good idea to use dashed lines for these rays because the light does not actually go behind the mirror, it just appears to. If the lines meet behind the mirror, the image is virtual. In this case, we can see that the image is virtual and upright. It's also a lot smaller than the original object.
It turns out that convex mirrors always produce the same kind of image, irrespective of where the original object is located. An image formed by a convex mirror will always be virtual, upright, and smaller than the object.
Original Content By: Study.com