CONVEX MIRROR

Rules of Reflection for Convex Mirror Any incident ray traveling parallel to 

the principal axis on the way to a convex mirror will reflect in such a manner that its extension will pass through the focal point.

Any incident ray traveling towards a convex mirror such that its extension passes through the focal point will reflect and travel parallel to the principal axis.

1. Pick a point on the top of the object and draw two incident rays traveling towards the mirror.

2. Once these incident rays strike the mirror, reflect them according to the two rules of reflectionfor convex mirrors.

3. Locate and mark the image of the top of the object.

4. Repeat the process for the bottom of the object.

Sample The diagrams above show that in each case, the image

is located behind the convex mirror a virtual image an upright image reduced in size (i.e., smaller than the object)

The Mirror Equation

The mirror equation expresses the quantitative relationship between the object distance (do), the image distance (di), and the focal length (f).

The Magnification Equation

The magnification equation relates the ratio of the image distance and object distance to the ratio of the image height (hi) and object height (ho). 

Sample ProblemA 4.0-cm tall light bulb is placed a distance

of 35.5 cm from a convex mirror having a focal length of -12.2 cm. Determine the image distance and the image size. 

GIVEN ho = 4.0 cm

do = 35.5 cm f = -12.2 cm UNKNOWNdi = ??? hi = ???

Solution and Answer

1/f = 1/do + 1/di

1/(-12.2 cm) = 1/(35.5 cm) + 1/di

-0.0820 cm-1 = 0.0282 cm-1 + 1/di

-0.110 cm-1 = 1/di

di = -9.08 cm

Assignment1. A convex mirror has a focal length of -10.8 cm. An

object is placed 32.7 cm from the mirror's surface. Determine the image distance.

2. Determine the focal length of a convex mirror that produces an image that is 16.0 cm behind the mirror when the object is 28.5 cm from the mirror.

3. A 2.80-cm diameter coin is placed a distance of 25.0 cm from a convex mirror that has a focal length of -12.0 cm. Determine the image distance and the diameter of the image.

4. A focal point is located 20.0 cm from a convex mirror. An object is placed 12 cm from the mirror. Determine the image distance.