Physics 1161 – Prelecture Physics 1161 – Prelecture 2323

Converging & Diverging Converging & Diverging LensesLenses

Shape of a LensShape of a Lens

Types of LensesTypes of Lenses

Lens TermsLens Terms

Three Rays to Locate Three Rays to Locate ImageImage

Ray parallel to axis bends through the focus. Ray through the focus bends parallel to axis. Ray through center of lens passes straight

through.

Characterizing the ImageCharacterizing the Image

Images are characterized in the following way1. Virtual or Real2. Upright or Inverted3. Reduced, Enlarged, Same Size

Object Beyond 2fObject Beyond 2f

Image is– Real– Inverted– Reduced

Object at 2fObject at 2f

Image is– Real– Inverted– Same size

Object Between 2f and fObject Between 2f and f

Image is– Real– Inverted– Enlarged

Object at FObject at F

No Image is Formed!

Object Closer than FObject Closer than F

Image is– Virtual– Upright– Enlarged

Converging Lens ImagesConverging Lens Images

Concave (Diverging) LensConcave (Diverging) Lens

Ray parallel to axis refracts as if it comes from the first focus.

Ray which lines up with second focus refracts parallel to axis.

Ray through center of lens doesn’t bend.

Image Formed by Concave Image Formed by Concave LensLens

Image is always– Virtual– Upright– Reduced

Concave Lens Image Concave Lens Image DistanceDistance

As object distance decreases– Image distance

decreases– Image size increases

Image CharacteristicsImage Characteristics

CONVEX LENS – IMAGE DEPENDS ON OBJECT POSITION– Beyond F: Real; Inverted; Enlarged,

Reduced, or Same Size– Closer than F: Virtual, Upright, Enlarged– At F: NO IMAGE

CONCAVE LENS – IMAGE ALWAYS SAME– Virtual– Upright– Reduced

Lens EquationsLens Equations

convex: f > 0; concave: f < 0 do > 0 if object on left of lens

di > 0 if image on right of lens otherwise di < 0

ho & hi are positive if above principal axis; negative below

1 1 1

o if d d

i i

o o

h dM

h d

do

di