physics xf: eyes

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    THE EYES

    *

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    INTRODUCTION OF EYESOOptical instrument

    O

    Have convex lensOHave the focal length so that

    objects can be seen.

    http://localhost/var/www/apps/conversion/tmp/scratch_10/Bill%20Nye%20The%20Science%20Guy%20on%20The%20Eyeball%20(Full%20Clip).flvhttp://localhost/var/www/apps/conversion/tmp/scratch_10/Bill%20Nye%20The%20Science%20Guy%20on%20The%20Eyeball%20(Full%20Clip).flvhttp://localhost/var/www/apps/conversion/tmp/scratch_10/Bill%20Nye%20The%20Science%20Guy%20on%20The%20Eyeball%20(Full%20Clip).flv
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    Parts of THE EYE

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    Cornea A transparent protective layer, which is

    located on the outer part of the eye.

    Can refract LIGHT.

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    Clear, watery and transparent fluid.

    Located behind the cornea.

    Refract the light.

    Aqueous Humor

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    Gives color to the eye Ex: blue, black, brown,green.

    Consists of muscular diaphragm.

    Controls the amount of light by dilating and constricting

    the pupil. It contracts and expands the pupil.

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    PupilO Hole in the center of the iris that light

    passes through.

    O Control the amount of light that enters the

    eye.O In bright light, the pupil constrict

    O In dim light, the pupil dilateIris muscle

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    Lens

    Made of transparent, fibrous and elastic layer.

    Held by the ciliary muscle changes the shapeof the lens and set the focal length.

    Continues refraction and focusing onto theretina.

    Have convex shape

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    Film of the eye. Rods and cones.

    Converts light rays and sends them to thebrain (optic nerves). Your vision is best when light falls on the

    fovea (blind spot).

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    Normal Eyes

    Normal eyes can see an object clearly that islocated at 25 cm to infinity.

    These distances are called near and far points ofnormal eyes.

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    LIKE

    THIS !

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    Short-Sighted (Myopia)

    Can see nearby objects clearly but distant

    objects appear blurred.

    Can be helped by concave lens

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    LIKE THIS GUY!

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    Example:O The far point for a man with short-

    sightedness is 318 cm. His glasses lens is

    2 cm in front of his eye,determine :a.The focal length that match to the

    person

    b.The optical power of the glasses.

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    Cant see close object clearly.

    The near point of farsighted patients is more

    than 25 cm.Can be helped by convex lens.

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    The near point of a person withfarsightedness is 48cm. In order to read a

    book 25 cm away (normal distance) , heuses a glasses. If the lens is 2 cm in frontof his eye, determine the focal lengthand the optical power of the glasses !

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    Cannot see the object that are too close or too far.

    Its because its near point is more than 25 cm and thefurthest point is less than infinity.

    Assisted with two types of lens.

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    CONVEX LENS Used when viewing near objects.

    EXAMPLE:

    While reading book or identifying the person in front

    of them.

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    Used when viewing distant object

    EXAMPLE:

    SEE THE MOUNTAINS OR A CAR FROM A

    DISTANCE

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    *Suppose the distance from the lens of aneye to the retina is 2 cm. Find the optical

    power of the eye accommodation when

    seeing a very distant and very closeobject.

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    CHECK YOUR

    UNDERSTANDING

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    LETS PRACTICE !

    Anita is said to suffer from myopia with farpoint 150 cm. what is the power of thespectacle lens in order that Anita canview object in far distance ?

    Known: = = 150

    Asked : P=? =?

    =

    +

    =

    + -

    = 0 + -

    = -150 cm = -1.5m =

    =

    .= -

    3D

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    A sufferer of far sighted has near point of 50 cm.

    What is the power of glasses lens that must be

    used so that the man can see things normally?

    Self Practice

    Known: = 25 = 50

    Asked : P=? =?

    =

    +

    =

    + -

    =

    =

    = 50 cm = + 0.5m =

    =

    . = + 2D

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    Self Practice Suppose that an eye-lens is on 2.5 cm in front of

    retina. Find the focal length and optical power, ifthe eye is used to observe an object on :a. the near point of the normal eyeb. infinity

    c. range of optical power of eye accommodationa. near point

    =

    +

    =

    +

    .

    =

    +

    =

    =

    cm =

    m

    =

    =

    = 44 D

    b. infinity

    =

    +

    =

    +

    .

    =

    .cm

    = 2.5cm =

    m

    =

    =

    = 40 D

    c. range optical power

    - = 44 D 40D

    = 4 D.

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