Lenses June 2010

Today  Lenses  Total Internal Reflection  Lab – Exploring Lenses  Next class:  Telescopes, rainbows & review

Lab Review  Light rays in are parallel to light rays out  What would happen if the light left the side?

Internal reflection  Consider light leaving glass into air:  It speeds up  It bends  “away from normal”  At some point it goes horizontal  The critical angle!  Beyond that angle…  TOTAL INTERNAL REFLECTION!

Fish-lights

Curved Medium - Glass  Consider an irregular shaped piece of glass…  As light enters it is bent towards the “normal”  If the glass is uniformly curved…  We call it a lens

Lenses  Lenses form images  Just like mirrors  Except it’s refraction (not reflection)  We use lenses a number of places  Telescopes, cameras, microscopes  Eyeglasses,  Even our eyes  How many of you wear glasses or contacts?  Near sighted or far sighted?

Types of lenses  Lenses have 2 sides  Each side can be curved or flat  We’ll focus (yuck, yuck, yuck…)  On lenses that are curved on both sides  2 types  Converging  Diverging

Let’s look at them…  How many focal points?  Images can be  Real or virtual  USD or RSU  Larger or smaller

We’ll simplify…  When we draw ray diagrams  Just draw the line to the center of the lens  From there – to wherever it should go

The Rules – Converging  Ray parallel to PA - Passes through to opposite “F”  Ray to center of lens - Continues same direction  Ray through near “F” - Parallel to PA

The Rules - Diverging  Ray parallel to PA - Away from near “F”  Ray to center of lens - Continues same direction  Ray through far “F” - To lens and parallel to PA

Corrective lens for myopia = concave (diverges light)

Myopia = nearsightedness  Elongated eyeball or bulging cornea results in images of distant object forming in front of retina.

Corrective lens for myopia = concave (diverges light)

Hyperopia = farsightedness  Shortened eyeball or flat cornea  Images from nearby objects form behind retina.  Often due to muscles not causing the lens to change shape (older people).

Corrective lens  Convex  converges light  Image forms closer to optic nerve

Lab!  Explore real images with lenses!

End of year announcements!  Late work deadline  Seniors: Monday 3 pm  All others: Wednesday 3 pm  Senior Final  60 – 80 questions  4 x 6 notecard, handwritten, both sides  AP Physics Class of 2011  Meeting here on Thursday at break  Mandatory

Rainbows and Telescopes!  What color is on the outside of a rainbow?  Where is the sun when you see a rainbow?  Have you ever seen colored rings around the moon?

Refracted light

Rainbows

Telescopes

Microscopes