Images formed by curved mirrors look different than those from flat mirrors.  The process of image formation, however, is easily demonstrated graphically by ray diagrams, or mathematically using equations, both of which obey the law of reflection.

 

Similar to flat mirrors, the real or virtual image produced by a curved surface can be described by magnification, attitude (erect or inverted), and position.  A curved mirror can be formed by cutting off a section of a spherical mirror.  The inside surface would be a converging mirror with a concave surface that reflects rays to a central focal point.  The outside surface would be a diverging mirror with a convex surface that causes the reflected light to spread out.  Refer to "Figure 13.38" on page 659 in your textbook.


  


Read
Read "Image Formation in a Curved Mirror" on page 657 of your textbook then, using "Figure 13.36" as a guide, complete the following table:


Term

Definition

centre of curvature (C)

 

radius of curvature ( r )

 

vertex (V)

 

principal axis (PA)

 

principal focal point (F)

 

focal length ( f )

 

 

Ray diagrams can be used to explain and predict how an image forms in a curved mirror.  Similar to that of a flat mirror ray diagram, several rays are sketched to determine the location, size, orientation, and type of image.  Generally, three rays are used to follow the path of the light.  Note that there are many rays that make the image, but only a few rays are required to identify its location and characteristics.
In the ray diagram for a concave mirror on the right, ray 1 travels parallel to the principal axis and is reflected through the mirror's focal point.  Ray 2 is incident to the mirror's vertex.  At the vertex, the surface of the mirror is perpendicular to the principal axis, so the angles of incidence and reflection are equal.  Ray 3 travels through the focal point and is reflected parallel to the principal axis.  These guidelines for drawing ray diagrams are summarized in the following table.
© F. Hwang, NTNU JAVA Virtual Physics Laboratory. Used with permission.

 

Ray Number

Incident Ray

Reflected Ray

1

parallel to principal axis

through F

2

to vertex

Θ r = Θ i

3

through F

parallel to principal axis

 

A real image is formed where the rays meet, or converge.  A virtual image is formed if the rays "appear" to have converged at some point.

 

The image in this figure is real (the light rays converge at the image), inverted (upside down relative to the object), diminished in size, and located beyond the focal point.