Conceptual Conceptual PhysicsPhysics

Notes on Chapter 30Notes on Chapter 30

Lenses

Lenses Lenses

Any piece Any piece of glass of glass that bends that bends parallel parallel rays of rays of light is a light is a Lens Lens

Lenses Lenses If the parallel rays come together If the parallel rays come together

than the lens is a than the lens is a Converging Converging LensLens

Lenses Lenses If the parallel rays spread apart, If the parallel rays spread apart,

then the lens is a then the lens is a Diverging LensDiverging Lens

Lenses Lenses

Three raysThree rays make up make up the primary rays the primary rays through a lens. through a lens. TwoTwo are needed to form are needed to form the image.the image.

Lenses Lenses MajorMajor ( (PrincipalPrincipal) ) axisaxis - Line that - Line that runs through the center of the lens.runs through the center of the lens.

a. a. Focal PointFocal Point ( (FF) is on this ) is on this line.line.

b. b. Focal LengthFocal Length is on this is on this line.line.

c. c. Center of curvatureCenter of curvature is on is on this line.this line.

LensesLensesRay #1Ray #1 goes through center of lens. goes through center of lens.

Ray #2Ray #2 starts out parallel to lens starts out parallel to lens and bends to focal point on other and bends to focal point on other side of lens.side of lens.

Ray #3Ray #3 goes through focal point to goes through focal point to lens and then parallel to major lens and then parallel to major axis.axis.

Lenses Lenses Ray #1 goes through center Ray #1 goes through center

of lensof lens..

LensesLenses Ray #2#2 coming in horizontally from the tip of the arrow, goes through the focal point.                                          

Lenses Lenses

Ray #3 going from the tip of the arrow to the near focal point will come out horizontally

LensesLenses

ImagesIf we combine the two we get the following picture.

                                                                              

Lenses Lenses REAL AND VIRTUAL IMAGESREAL AND VIRTUAL IMAGES

Real imagesReal images are formed when the are formed when the object is far enough away to be object is far enough away to be beyond beyond the focal pointthe focal point to be focused on a to be focused on a screen.screen.

Virtual imagesVirtual images appearappear to be behind the to be behind the glass - but there is no light behind the glass - but there is no light behind the glassglass

(Mirror is a good example)(Mirror is a good example)

Lenses Lenses

The Eye:The Eye: PartsParts

IrisIris PupilPupil CorneaCorneaRetinaRetina

Lenses Lenses Defects called Defects called FarsightedFarsighted and and NearsightedNearsighted can can cause your cause your vision to be vision to be blurred.blurred.

Lenses Lenses FarsightedFarsighted people see people see

images blurred due to lens images blurred due to lens making the image form making the image form “behind” the retina.“behind” the retina.

Lenses Lenses NearsightedNearsighted people see people see

images blurred due to lens images blurred due to lens making the image form making the image form before the retina.before the retina.

Lenses Lenses Other defects can be Other defects can be Spherical Spherical

AberrationAberration. All parallel rays . All parallel rays do do notnot converge to one single point. converge to one single point.

Lenses Lenses Chromatic AberrationChromatic Aberration is is

do to different colors and do to different colors and speeds in lenses.speeds in lenses.