Ch 18 Notes

1. Ch 18
Mirrors and Lenses

2. Plane Mirror
 flat, smooth surface that
reflects light in a regular
way;
 it produces an image that
is virtual, erect, and the
same size as the object;
 left and right appear to
be interchanged, but
front and back are
interchanged

3. Types of Images
 Real image - source of converging light rays; can
be projected; are always inverted
 Virtual image - source of diverging light rays;
cannot be projected; are always erect

4. Concave Mirror
 reflects light off its inner surface
 Focal point - (f) point on the principle axis where
reflecting light converges;
 f equals one-half the radius of curvature (C)

5. Spherical Aberration
 defect of all spherical mirrors when the parallel rays
don’t all reflect through the focal point;
 correct this by using a parabolic mirror

6. Concave Mirror Characteristics
 If the object is outside C,
the image is real,
inverted, and smaller

7. Concave Mirror Characteristics
 If the object is at C, the
image is real, inverted,
and the same size

8. Concave Mirror Characteristics
 If the object is between
C and f, the image is real,
inverted, and larger

9. Concave Mirror Characteristics
 If the object is inside f,
the image is virtual, erect,
and larger

10. Mirror Equation
 1 = 1 + 1 or di = f x do
f do di do – f
 f is the focal length
 do is the object distance
 di is the image distance
 magnification - the ratio of the image size (hi) to the
object size (ho)
 m = hi = - di
ho do

11. Mirror Equation Rules
 di is positive for real images, negative for virtual
images
 hi is positive for erect images, negative for
inverted images
 f is positive for concave mirrors, negative for
convex mirrors

12. Convex mirror
 reflects light off the
outer surface
 images are always virtual,
erect, and smaller
 these are used as safety
mirrors because you get a
wider angle of vision

13. Lens
 transparent material with a refractive index
larger than air
 The focal length of the lens depends on the
shape and refractive index of the material

14. Convex Lens
 Convex lens - (converging lens) thicker in the
middle than at the edges; acts like a concave
mirror.
 Chromatic aberration - caused when light passes
thru the edge of a lens; the light is dispersed;
correct using an achromatic lens

15. Convex Lens Characteristics
 Outside 2f, image is real,
inverted, and smaller

16. Convex Lens Characteristics
 At 2f, image is real,
inverted, and same size

17. Convex Lens Characteristics
 Between 2f and f, image
is real, inverted, and
larger

18. Convex Lens Characteristics
 Inside f, image is virtual,
erect, and larger

19. Concave lens
 (diverging lens) thinner
in the middle than at the
edges
 acts like a convex
mirror.
 Always produces virtual,
erect, and smaller image

20. Lens Equation Rules
 The equation and rules stay the same except f is
positive for convex lens and negative for
concave lens

21. Corrective Lenses

22. Near-Sighted People
 have too short a focal length
 correct this using a concave (diverging) lens

23. Far-Sighted People
 have too long a focal length,
 correct this using a convex (converging) lens