LensesLenses

June 2010June 2010

TodayToday

LensesLenses Total Internal ReflectionTotal Internal Reflection Lab – Exploring LensesLab – Exploring Lenses Next class: Next class:

Telescopes, rainbows & reviewTelescopes, rainbows & review

Lab ReviewLab Review

Light rays in are Light rays in are parallel to light rays parallel to light rays outout

What would happen What would happen if the light left the if the light left the side?side?

Internal reflectionInternal reflection

Consider light leaving glass into air:Consider light leaving glass into air: It speeds upIt speeds up It bends It bends

““away from normal”away from normal” At some point it goes horizontalAt some point it goes horizontal

The critical angle!The critical angle! Beyond that angle…Beyond that angle…

TOTAL INTERNAL REFLECTION!TOTAL INTERNAL REFLECTION!

Fish-lightsFish-lights

Curved Medium - GlassCurved Medium - Glass

Consider an irregular shaped piece of Consider an irregular shaped piece of glass…glass…

As light enters it is bent towards the As light enters it is bent towards the “normal”“normal”

If the glass is uniformly curved…If the glass is uniformly curved… We call it a lensWe call it a lens

LensesLenses

Lenses form imagesLenses form images Just like mirrorsJust like mirrors Except it’s refraction (not reflection)Except it’s refraction (not reflection)

We use lenses a number of placesWe use lenses a number of places Telescopes, cameras, microscopesTelescopes, cameras, microscopes Eyeglasses, Eyeglasses, Even our eyesEven our eyes

How many of you wear glasses or contacts?How many of you wear glasses or contacts? Near sighted or far sighted?Near sighted or far sighted?

Types of lensesTypes of lenses

Lenses have 2 sidesLenses have 2 sides Each side can be curved or flatEach side can be curved or flat

We’ll focus (yuck, yuck, yuck…)We’ll focus (yuck, yuck, yuck…) On lenses that are curved on both sidesOn lenses that are curved on both sides

2 types2 types ConvergingConverging DivergingDiverging

Let’s look at them…Let’s look at them…

How many focal points?How many focal points? Images can be Images can be

Real or virtualReal or virtual USD or RSUUSD or RSU Larger or smallerLarger or smaller

We’ll simplify…We’ll simplify…

When we draw ray diagrams When we draw ray diagrams Just draw the line to the center of the lens Just draw the line to the center of the lens From there – to wherever it should goFrom there – to wherever it should go

The Rules – ConvergingThe Rules – Converging

Ray parallel to PA - Passes through to opposite “F”Ray parallel to PA - Passes through to opposite “F” Ray to center of lens - Continues same directionRay to center of lens - Continues same direction Ray through near “F” - Parallel to PARay through near “F” - Parallel to PA

The Rules - DivergingThe Rules - Diverging

Ray parallel to PA - Away from near “F”Ray parallel to PA - Away from near “F” Ray to center of lens - Continues same Ray to center of lens - Continues same

directiondirection Ray through far “F” - To lens and parallel to PARay through far “F” - To lens and parallel to PA

Corrective lens for Corrective lens for myopia = concave myopia = concave (diverges light)(diverges light)

Myopia = Myopia = nearsightednessnearsightedness

Elongated eyeball or bulging cornea Elongated eyeball or bulging cornea results in images of distant object results in images of distant object forming in front of retina.forming in front of retina.

Corrective lens for Corrective lens for myopia = concave myopia = concave (diverges light)(diverges light)

Hyperopia = Hyperopia = farsightedness farsightedness

Shortened eyeball or flat cornea Shortened eyeball or flat cornea Images from nearby objects form behind retina. Images from nearby objects form behind retina. Often due to muscles not causing the lens to Often due to muscles not causing the lens to

change shape (older people). change shape (older people).

Corrective lensCorrective lens

Convex Convex converges lightconverges light Image forms closer Image forms closer

to optic nerveto optic nerve

Lab!Lab!

Explore real images with lenses!Explore real images with lenses!

End of year End of year announcements!announcements!

Late work deadlineLate work deadline Seniors: Monday 3 pmSeniors: Monday 3 pm All others: Wednesday 3 pmAll others: Wednesday 3 pm

Senior FinalSenior Final 60 – 80 questions60 – 80 questions 4 x 6 notecard, handwritten, both sides4 x 6 notecard, handwritten, both sides

AP Physics Class of 2011AP Physics Class of 2011 Meeting here on Thursday at breakMeeting here on Thursday at break MandatoryMandatory

Rainbows and Rainbows and Telescopes!Telescopes!

What color is on the outside of a What color is on the outside of a rainbow?rainbow?

Where is the sun when you see a Where is the sun when you see a rainbow?rainbow?

Have you ever seen colored rings around Have you ever seen colored rings around the moon?the moon?

Refracted lightRefracted light

RainbowsRainbows

TelescopesTelescopes

MicroscopesMicroscopes