Lenses ppt

7/29/2019 Lenses ppt

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Lenses

Converging

LensDiverging

Lens

F F

ff


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Find the focal length of a converging lens byholding it up to a window.

(See how far away from the lens you need to holda piece of paper to focus the image on the paper.)

Web Link: Spherical mirrors and lenses
http://surendranath.tripod.com/Applets/Optics/ReflRefrCurv/CurvSurfApplet.htmlhttp://surendranath.tripod.com/Applets/Optics/ReflRefrCurv/CurvSurfApplet.html


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Ray Tracing for Lenses

Light passes through a lens

There is a focal point on both sides of a lens

Converging Lens:

Ray #1:Parallel to the axis

Refracts through F

Ray #2:Through F

Refracts parallel to axis

Ray #3:Through Center of

lens undeflected


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Example: Camera


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Example: Slide Projector


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Example:

MagnifyingGlass Web Link:

Ray tracing
http://www.phy.ntnu.edu.tw/java/Lens/lens_e.htmlhttp://www.phy.ntnu.edu.tw/java/Lens/lens_e.html


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Results: Ray Tracing for Converging Lenses(in each case, draw in the 3 rays for practice)

Object distance > 2f: Image is real, smaller, and inverted

FF2F

Object between f and 2f: Image is real, larger, inverted

FF2F

Object between f and mirror: Image virtual, larger, upright

FF2F


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Ray #1: Parallel to the axis on the leftRefracts as if it came from F on the left

Ray #2: Heads toward F on the right

Refracts parallel to the axis on the right

Ray #3: Through the center of the lens undeflected

Web Link: Spherical mirrors and lenses

Now, for Diverging lenses

For a Diverging Lens:
http://surendranath.tripod.com/Applets/Optics/ReflRefrCurv/CurvSurfApplet.htmlhttp://surendranath.tripod.com/Applets/Optics/ReflRefrCurv/CurvSurfApplet.html


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2

Example: Glasses to correct nearsightedness


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Results: Ray Tracing for Diverging Lenses(draw in the 3 rays for practice)

No matter where the object is:Image is always virtual, smaller and upright

FF

Web Link:Ray Tracing Summary for

Mirrors and Lenses

Web Link: Ray tracing
http://www.sciencejoywagon.com/physicszone/lessonch/09waves/optics/raytrace/default.htmhttp://www.sciencejoywagon.com/physicszone/lessonch/09waves/optics/raytrace/default.htmhttp://www.phy.ntnu.edu.tw/java/Lens/lens_e.htmlhttp://www.phy.ntnu.edu.tw/java/Lens/lens_e.htmlhttp://www.sciencejoywagon.com/physicszone/lessonch/09waves/optics/raytrace/default.htmhttp://www.sciencejoywagon.com/physicszone/lessonch/09waves/optics/raytrace/default.htm


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For a lens, a real imageis on the opposite side

as the object

1

d

1

d

1

fo i

The Thin LensEquation

md

d

i

o

These equations also work on lenses:

The MagnificationEquation

But the variables are defined slightly differentlynow because.

For a mirror, a realimage was on the same

side as the object


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Sign conventions for Lenses

Focal length (f)+ converging

- diverging

Object distance (do)

+ object on the left

Image distance (di)

+ image on the right (real)

- image on the left (virtual)

Magnification (m)

+ upright

- inverted


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Ex:

lens

book

13cm

If the image of the book is 5.0 cm belowthe lens, find the focal length of the lens.


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Ex:

A camera with a focal length of 50 mm takes a

photograph of a 100 m tall building from 350 maway. How tall is the image on the film?


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The Human Eye

Web Links: Eye lens,Vision and Eyesight

Near Point Closest distance the

eye can focus on(about 25 cm when

we are young)

Far Point Farthest distance

the eye can focuson (should be )
http://micro.magnet.fsu.edu/primer/java/eyeball/index.htmlhttp://www.sciencejoywagon.com/physicszone/lessonch/09waves/optics/eyes/index.htmhttp://www.sciencejoywagon.com/physicszone/lessonch/09waves/optics/eyes/index.htmhttp://micro.magnet.fsu.edu/primer/java/eyeball/index.html


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Someone who is Nearsighted cannotfocus on far away objects. (Their

far point is not at infinity.)

Nearsightedness can be correctedwith diverging lenses

Heres how it works


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Ex:

Without my contact lenses, I need to stand 35 cm orless from the TV in order to see it in focus. Find the

focal length of the contact lenses that correct my

vision.


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Someone who is Farsighted cannotfocus on objects too near.

Farsightedness can be corrected with

converging lenses

Heres how it works


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The man has a near point of 48 cm. Hisreading glasses are 2.0 cm from his eyes,

and with them on, he can read the

newspaper as close as 25 cm to his eyes.Find the focal length of his glasses

Ex:


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Lens Aberrations

1) Spherical Aberration

Can you think of two ways that thisproblem could be eliminated?


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2) Chromatic Aberration

How to correct this problem?

Compound(Achromatic)

Lens

Lenses ppt

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