GEOMETRIC OPTICS PRINCIPLES

PART 1--MIRRORS

IMAGES FORMED BY PLANE MIRRORS
  • The image is always as far behind the mirror as the object is in front.
  • The image is unmagnified, virtual and upright. (Note: Virtual images are images forms at a point where light APPEARS to diverge from the image point but does not actually come from that point, Virtual images appear as upright --the same orientation as the object.)
  • The image has right-left reversal.

    IMAGES FORMED BY SPHERICAL MIRRORS OF FOCAL LENGTH "f"

  • The image may be a real image in a concave mirror if the object distance "o" is greater than the focal distance f. If real, the image is reduced in size if "o" is greater than 2f . If real, the image is enlarged for "o" less than 2f but greater than f. (Note: Real images are formed at a point in space where reflected light actually intersect and diverge from the image position.) All the real images appear on the same side of the mirror as the FOCUS.
  • The image is a virtual image in a concave mirror if "o" is less than f. In this case the image will be enlarged, upright and virtual. It will be located behind the mirror instead of in the actual space in front of the mirror.
  • All convex mirrors from virtual images. These images are always reduced in size, upright, and located behind the mirror

 

RAY TRACING RULES:

  1. A ray coming from the OBJECT that is PARALLEL to the AXIS (line perpendicular to center of mirror or lens) will reflect (or refract) out through F--the FOCUS. This ray is drawn in blue below.
  2. A ray coming from the object that is directed toward F--the FOCUS--will reflect (or refract out PARALLEL to the axis. This is the GREEN ray.
  3. A ray in through 2f --R--will reflect out on top of itself (mirror only--RED ray). For a lense, the ray though the Optic Center of the lens passes through without bending.

 

LOCATING IMAGES WITH RAY DIAGRAMS
TYPE

CONCAVE MIRROR

O, i, f, R all positive

IMAGE--REAL, INVERTED

CONCAVE MIRROR

O, f, R   positive

i negative!

IMAGE-- virtual, upright, enlarged

 

CONVEX MIRROR

o positive

i, f, R--negative

IMAGE-- Virtual, upright & smaller

 

 

THE MIRROR/ LENS EQUATION

SIGNS ARE IMPORTANT!

"o" = distance from object to middle of mirror

"i" = distance form image to middle of mirror

"f" = distance from FOCUS to middle of mirror

R = 2f

"f" is ALWAYS negative for a convex mirror and concave lens.

In this diagram you see how "o", "i" and "f" are measured.

 

O = Height of OBJECT

I = Height of IMAGE

Magnification= O/ I

 

 

VIRTUAL OPTICS LAB

LIGHTSITE

LIGHT

VIRTUAL LABS

WAVE OPTICS

A LOOK AT IMAGES

LENSES & RAY TRACING

 

REVIEW OF CONCEPTS

OPTICS LESSONS

EXCELLENT QUIZ ON OPTICS