IMAGES IN A MIRROR
THESE MIRRORS ARE PLASTIC, AND CAN BE SCRATCHED. TRY NOT TO TOUCH THEM. THANK YOU.
Look at your reflections in the flat and outward curving or convex mirror.
Stand about three feet away from the flat mirror. How much of your surroundings do you see reflected? Now stand about three feet away from the convex mirror. How much of your surroundings do you see reflected?
Lean towards and away from each mirror. What do you notice about your reflections.
There should be a ruler at the exhibit. Hold the ruler up to each of the mirrors.
The outward curving or convex mirror distorts images. A flat mirror accurately reflects images.
Because of the way a convex mirror distorts, you look smaller. Your brain interprets this as meaning that the image in the mirror is further away than it really is.
When a ray of light hits a flat mirror, it makes an angle with the surface of the mirror, called the angle of incidence. It reflects off the mirror at an identical angle of reflectance.
This fact that the angle of incidence equals the angle of reflectance determines how much of the surroundings we can see in a flat mirror, or what is called the field of view.
The same rules regarding angles are true for convex mirrors, but finding the angles is a little more involved because the surface of the mirror is curved.
A tangent only touches a curved surface at one point. Think of a ping pong ball resting on a table. The table is only touching the ball at one point and is therefore a tangent to the ping pong ball at that point. A two dimensional curved surface, such as a circle, has tangent lines to points on the circumference of the circle. A three dimensional curved surface, such as a ping pong ball, has a tangent plane at each point on its surface.
A ray of light strikes a curved mirror at a particular point. Imagine a tangent line to the curved mirror through that point. The angle of incidence the ray of light makes with that tangent line will equal the angle of reflectance with that same tangent line.
With convex mirrors, many more objects on your left and right can be seen than with flat mirrors. The area that you can see in a mirror is called the field of view. The convex mirror has a much greater field of view.
Most mirrors in your home are flat mirrors so that the reflected image is accurate. Many automobiles have outside mirrors on the doors. The passenger side mirror is often a convex mirror so that you can see more of the area to the right of the car.
The simplest example of a curved mirror in the home is a silver Christmas tree ornament. An example of a differently shaped convex mirror is a metal drain pipe for kitchen sinks. These "mirrors" are cylinders and can be purchased for little money at hardware and plumbing supply stores.
Why would a convex mirror on the passenger door of a car be labeled "Objects may be closer than they seem?"
The images of objects reflected in the convex mirror will be smaller than the images reflected in a flat mirror. Our brains have become adopted to seeing and interpreting images in flat mirrors. When we see an image in a convex mirror our brain will treat it as an image in a flat mirror. Since it is smaller our brain will assume that the image is farther away.
Convex mirrors are sometimes seen along roadways and in buildings when hallways intersect. Why do you think convex mirrors are used here instead of flat mirrors?
The convex mirror has a much greater field of view, meaning that people can see much more to their left and right than they could with a flat mirror. The convex mirror allows you to see cars and people approaching from the sides.
You want to try to determine how much your image is distorted by a convex mirror. You are exactly three feet tall so you hold a yardstick alongside you and look at your image in a convex mirror. Will this let you measure the amount of distortion?
No. The image of the yardstick will be distorted too.
What is the effect on a reflected image of increasing the curvature of a convex mirror? What is the effect on the field of view of increasing the curvature of a convex mirror?
A convex mirror with a greater curve will produce a more distorted image. It will also increase the field of view, allowing you to see more to your left and right.
The convex mirror is held on with five clips equally spaced around a circle. How can you divide a circle into five equal parts?
There are at least two ways to divide a circle into five equal parts. One way would use a compass scale indicating degrees from zero to 180. There 360 degrees in a complete circle. Five equal divisions of a circle would each have 72 degrees.
The second way to divide a circle into five equal parts involves trial and error, but is perhaps more accurate. On a straight edge such as a yardstick, mark off a distance slightly longer than the radius of the circle. Make a mark on the circumference of the circle - this is your starting point. Using your straightedge, hold one end of your distance on this starting point and make a mark on the circle where the other end of your distance crosses the circle. This is then your new starting point. Continue around the circle. If you don't finish on your first circumference mark, adjust your straightedge distance and repeat the process.
challenge question 6 needed
challenge question 6 answer
challenge question 7 needed
challenge question 7 answer
topics involved listing needed
further information listing needed
This exhibit was inspired by the Spherical Reflections exhibit.
Top of this page.
Return to GCSEC Sample Exhibits Page
GCSEC Home Page
Hosting of this site is generously provided by Choice.Net