Real vs Virtual Images
4/1/15
Real Image: Real images are formed where light rays converge (come together). Real images are always inverted (upside
down). Concave mirrors and converging (convex) lenses can form real images.
Convex Lens ray diagram:
Ist line: From top of object, draw line to center of lens, then through the focal point on the other side.
2nd line: From top of object, draw line through focal point to the lens, then parallel to the axis.
The image will be inverted – this is a real image.
Virtual Image: virtual images are formed where light rays appear to converge. Virtual images are always upright. Convex
mirrors, plane mirrors, divergent lenses from virtual images.
Plane mirror:
Өi
Normal
Өr
Law of reflection:
Өi = Өr
Example:
A convex lens has a focal length of 10 cm. An 8 cm tall pencil is upright 29 cm away from the lens.
Find the image distance.
1/f =1/di + 1/do
1/10cm = 1/di = 1/29cm
1/di = 0.0655
di = 15.26 cm
Find the magnification:
M = -di/ do
M = -15.26cm/ 29cm
M = -0.53
Find the height of the image:
M = hi/ ho
-0.53 = hi/ 8cm
Hi = -4.2 cm
Draw a ray diagram: