We see objects because one of two phenomena is at work. Either a) the object is luminescent and gives off its own light; or b) the object reflects light from other sources. Most objects fall into category b) and reflect light irregularly because they have rough and uneven surfaces. This is called diffuse reflection. But when the surface is smooth and formed into some regular shape, the direction that reflected light takes becomes very predictable.

 The first law. The incident ray, the reflected ray, and the normal line all lie in the same plane. This statement determines plane in which the reflected ray exists. At the point of incidence of the incoming ray on the mirror, we created normal (perpendicular) line which of necessity intersects the incident ray. [There is a theorem in geometry that states to two intersecting straight lines determine a plane.] The first law suggests that reflected ray must lie in this plane The second law. The angle reflection is equal to the angle of incidence. The incident ray and the normal line make some angle measured from the normal. Of all the angles possible between the reflected ray and the normal line, only one is permitted. the diagram above is intended to show rays of light leaving an object situated in the lower left corner. The red ray and blue ray leave the object and are diverging. They strike the mirror [represented by the green line], obey the laws of reflection, and continue to diverge. If they are intercepted by an eye in the upper left-hand corner, the eye may think that they are coming not from a point in the lower left but from some point on the lower right hand corner of the diagram. The eye is fooled because in all cases it would appear that light travels in straight lines. the last time the eye saw rays diverging is such a way, they were diverging from points behind the mirror.

 O-01 http://id.mind.net/~zona/mstm/physics/light/rayOptics/reflection/reflection1.html 361 Visit  HYPERPHYSICS  and check out this topic. 368 The usual fine treatment from Glenbrook http://www.glenbrook.k12.il.us/gbssci/phys/Class/refln/u13l3a.html Interesting sidebars from the Exploratorium http://www.exploratorium.edu/snacks/iconreflection.html Good stuff from ASU http://acept.la.asu.edu/PiN/rdg/reflection/reflection.shtml

 O-02 http://www.phy.ntnu.edu.tw/java/optics/mirror_e.html mirror game http://www.phy.ntnu.edu.tw/java/optics/mirrorgame_e.html multiple reflections with two mirrors http://www.phy.ntnu.edu.tw/java/index.html /applets/planmir/Welcome.html http://micro.magnet.fsu.edu/primer/java/scienceopticsu/hinged/index.html Plane mirror applet by Prof. Hershfeld http://www.phys.ufl.edu/~phy3054/light/mirror

Image Formation

Mirrors (and lenses as we shall see later) can form two different kinds of images - virtual images and real images. Their collected properties are listed in the table here.

 Virtual image Real Image Formed by mental extension of rays Formed by converging rays Cannot be projected on a screen Can be projected on a screen Not inverted Inverted Perverted Not perverted

When light leaves an object, the rays travel by diverging from the object. Placing a plane mirror near some object will redirect the rays to a new path; nevertheless, the rays continue to diverge. If these rays are intercepted by your eye, your brain recognizes this pattern of diverging rays and mentally extends them straight back to some point on the other side of the mirror glass. Hence the image appears to be behind the mirror. This kind of image is called a virtual image (no, there is no connection to virtual reality) and possesses the properties shown in the box above. These properties come in an unbreakable set; if one property is true, they are all true.

CURVED MIRRORS

A curved mirror can yield results that are quite different from the images produced by a plane mirror. Most commonly in an introductory course such as this, we deal with concave spherical mirrors. Picture a basketball about a meter in diameter. We coat the inside of the sphere with a reflecting surface and then (mentally anyway - this is not an industrial process) we cut out a piece using a cookie cutter. This mirror produces a different kind of image than does a plane mirror. Rays of light leave some point on an object and diverge on their way to the mirror. Having struck the mirror, they converge to a point in space. From that point rays continue diverging to the observer's eye. This is an example of a real image. See the list of properties for real images.actually whether a real images produced or not depends upon distance from object to mirror. Under certain circumstances in concave spherical mirror can produce an enlarged virtual image

if you coat the outside of the basketball, a convex spherical mirror is produced. this kind of a late if the mirror produces only virtual images and a smaller than you can be created a they have limited use The rules that govern where and what kind of image will be formed for all three mirrors are summarized on the page called mirror conventions.

Applets aweigh
 O-03 concave mirror applets http://www.phys.ufl.edu/~phy3054/light/mirror/applets/cavemir/Welcome.html http://webphysics.davidson.edu/Applets/Applets.html convex mirror applets http://www.phys.ufl.edu/~phy3054/light/mirror/applets/convmir/Welcome.html http://theory.uwinnipeg.ca/physics/java/java/dmirr/index.html http://www.lightlink.com/sergey/java/java/dmirr multiple application applets

If we place an object in front of a concave mirror and sufficiently far from the mirror, we find appearing in space in front of the mirror (and not behind it like the virtual images) an image that is inverted. We call this kind of image a real image, the properties of which are listed in the box above. As before, the rays leaving the object are diverging-they leave the object never expecting to see each other again. But because the mirror is curved the way it is, the rays come together at a point in front of the mirror. the rays pass through this image point and then diverge from there on their way to nowhere in particular. if those now newly diverging rays are intercepted by someone's eye, the eye and brain will conclude that there is something at the image point. There is a mathematical relationship that governs where the image will be located; it's called the Gaussian mirror formula and looks like this

In this formula do is the distance from object to mirror, di is the distance from image to mirror and R is the radius of curvature. Click here for the derivation.The rules governing the algebraic signs for these distances are given in the mirror conventions page.