Color Deficiency. Why do we see certain colors? We perceive only the reflected colors

Color Deficiency

Why do we see certain colors? We perceive only the reflected

colors.

Color by TransmissionThe color of a transparent

object is due to the color that it transmits

The material that absorbs colored light is known as pigment.

PigmentSelectively absorbs some

light frequencies while other frequencies are emitted.

This process of absorbing light is known as a subtractive process

Total Reflection or AbsorptionWhite is a

combination of all colors of light being reflected.

Black is the absence of light, all light is being absorbed.

http://cnx.org/content/m15131/latest/

Transmitted VS Absorbed

Primary colors of Pigment As a child you were

taught that red, yellow & blue were the primary colors, however cyan, magenta and yellow are the most useful when color mixing.

http://home.att.net/~RTRUSCIO/MIXITUP.htm

Primary Colors of PigmentMix red, green and blue paint

and the result is muddy brown.

Color printing is achieved by using magenta, cyan, yellow and black ink

http://home.att.net/~B-P.TRUSCIO/COLOR.htm

Subtractive Primary Colors of Pigment

Pigments reflect the color they are as well as other colors to either side of them on the visible spectrum.

Subtractive PrimariesCMYK

Cyan, Magenta and YellowPrint

Cyan is light with a wavelength between green and blue or a combination of green and blue light. Cyan pigment will absorb the red and

reflect green and blue or cyan colored light.

Lenses

A thin lens consists of a piece of glass or plastic, ground so that each of its two refracting surfaces is a segment of either a sphere or a plane

Lenses are commonly used to form images by refraction in optical instruments (cameras, telescopes, etc.)

Lenses - Refraction

There two types of lenses - Convex and Concave

Thin Lens Shapes (Convex) converging lenses They have positive

focal lengths They are thickest in

the middle Produces a real

image- refracted light rays do cross at the focal point

More Thin Lens Shapes (Concave) diverging lenses They have negative

focal lengths They are thickest at the

edges Produces a virtual

image- refracted light rays do not cross

Atmospheric Refraction and Sunsets

Light rays from the sun are bent as they pass into the atmosphere

It is a gradual bend because the light passes through layers of the atmosphere Each layer has a

slightly different index of refraction

The Sun is seen to be above the horizon even after it has fallen below it

Atmospheric Refraction and Mirages

A mirage can be observed when the air above the ground is warmer than the air at higher elevations

The rays in path B are directed toward the ground and then bent by refraction

The observer sees both an upright and an inverted image

Eyes and EyeglassesWhat type of lens do we have

in our eyes?Why do we have problems

seeing?What can we do to correct

those problems?

SEEING LIGHT - THE EYE

Cornea - does most of the focusing

Iris -

Pupil -

has the eye color and controls light intensity

Lens -

the hole in the eye

does remainder of focusing

Retina - location of light sensors, has rods and cones

Blind spot -

Fovea - center of vision, predominantly cones

optic nerve exit, no light sensors

NearsightednessAlso called myopia, defect of vision in which far objects appear blurred but near objects are seen clearly.

The image is focused in front of the retina rather than upon it.

Corrective eyeglasses with concave lenses compensate for the refractive error and help to focus the image on the retina.

Focal pointReflected lightenters eye

Nearsightedness

Farsightedness also known as hyperopia

A condition in which far objects can be seen easily but there is difficulty in near vision.

The image is focused behind the retina of the eye rather than upon it.

Corrective eyeglasses with convex lenses compensate for the refractive errors.

Focal pointbehind retina Reflected light

enters eye

Farsightedness

Astigmatism…pronounced as: stigmatizm

A type of faulty vision caused by a non-uniform curvature in the refractive surfaces-usually the cornea, less frequently the lens-of the eye.

As a result, light rays do not all come to a single focal point on the retina. Instead, some focus on the retina while others focus in front of or behind it.

Vision is blurred. A special cylindrical lens is placed in theout-of-focus axis to correct the condition.

Astigmatism

Mirrors

any shiny smooth surface

three types of mirrorsconvex, concave,

and plane

Mirror Symbolsf = focal lengthp = distance between object and mirrorq = distance between image and mirror

ho = height of object

hi = height of image

M = magnification = hi / ho

http://sol.sci.uop.edu/~jfalward/reflection/reflection55.html

Notations and Flat Mirror

The object distance is the distance from the object to the mirror or lens Denoted by p

The image distance is the distance from the image to the mirror or lens Denoted by q

The lateral magnification of the mirror or lens is the ratio of the image height (h ’) to the object height (h) Denoted by M (=h’/h)

Types of Images for Mirrors and Lenses

A real image is one in which light actually passes through the image pointReal images can be displayed on screens

A virtual image is one in which the light does not pass through the image pointThe light appears to come (diverge) from

that pointVirtual images cannot be displayed on

screens

Mirror Images

Real Image Image that is formed

by converging light rays that can be displayed onto a screen.

EX: rays of light from an overhead projector

Virtual Image Image formed through

reflection or refraction. Can be seen by the

observer, but cannot be projected onto a screen

EX: plane mirror image

More About Images

To establish where an image is formed, it is always necessary to follow at least two rays of light as they reflect from the mirror. The image formed by the flat mirror is a virtual image

Object distance Image distance

Flat Mirror

Simplest possible mirror Properties of the image

can be determined by geometry

One ray starts at P, follows path PQ and reflects back on itself

A second ray follows path PR and reflects according to the Law of Reflection

p=q!

Properties of an Image Formed by a Flat Mirror The image is as far behind the

mirror as the object is in frontp = q

The image is unmagnified, M=1 The image is virtual The image is upright

It has the same orientation as the object

There is an apparent left-right reversal in the image


Application – Day and Night Settings on Car Mirrors

With the daytime setting, the bright beam of reflected light is directed into the driver’s eyes

With the nighttime setting, the dim beam (D) of reflected light is directed into the driver’s eyes, while the bright beam goes elsewhere

Spherical Mirrors

A spherical mirror has the shape of a segment of a sphere

A concave spherical mirror has the silvered surface of the mirror on the inner, or concave, side of the curve

A convex spherical mirror has the silvered surface of the mirror on the outer, or convex, side of the curve

Concave Mirror, Notation

The mirror has a radius of curvature of R

Its center of curvature is the point C

Point V is the center of the spherical segment

A line drawn from C to V is called the principle axis of the mirror

I is the image point

Image Formed by a Concave Mirror, cont.

h ’ is negative when the image is inverted with respect to the object

p

q

h

h'M

Focal Length Incoming rays are

essentially parallel In this special case, the

image point is called the focal point

The distance from the mirror to the focal point is called the focal length The focal length is ½ the

radius of curvature f = R/2

Focal Point and Focal Length, cont.

The focal point depends solely on the curvature of the mirror, not by the location of the object

With f=R/2, the mirror equation can be expressed as

fqp

111

Sign Conventions for MirrorsQuantity Positive When Negative

When

Object location (do)

Object is in front of the mirror

Object is behind the mirror

Image location (di)

Image is in front of mirror (real)

Image is behind of mirror (virtual)

Image height (h’) Image is upright Image is inverted

Focal length (f ) and radius (R)

Mirror is concave Mirror is convex

Magnification (M) Image is upright Image is inverted

Focal Length Shown by Parallel Rays

Concave Mirror The center of this

mirror curves away from you.

This means that with the law of reflection the reflected light rays will cross producing a real image.

Images produced with Concave Mirror

do = C : real inverted image, same size do = F : no image is seen

If object is past C:

Real, inverted, reduced image is formed

If object is between C and F: real, inverted, large image is produced

If in front of F: virtual, upright, enlarged image is produced

C F

Convex Mirrors

A convex mirror is sometimes called a diverging mirror

The rays from any point on the object diverge after reflection as though they were coming from some point behind the mirror

The image is virtual because it lies behind the mirror at the point where the reflected rays appear to originate

In general, the image formed by a convex mirror is upright, virtual, and smaller than the object

Image Formed by a Convex Mirror

Convex Mirrorcurves outwards in the middleproduces an image that is virtual,

upright and smaller than the objectReflected light rays never meet so they cannot produce a real image

Objects in mirror are closer than they appear

The Mirror Equation 1/do + 1/di = 1/f (1)-------------------------- Convex: f is negative--------------------------

Object distances are always positive for all types of mirrors.

do is positive ------------------------------ 1/di= 1/f - 1/do (2) = neg - pos = negative di is negative

Magnification Equation: M = -di / do (3)------------------------------------ M = -(negative)/positive = positive

Image is upright-----------------------------------From (2), we see that themagnitude of 1/di is alwayslarger than 1/do, so themagnitude of di is alwayssmaller than do:

M is always less than onefor a convex mirror.


Convex Mirror

Concave vs. Convex

Ray Diagrams

A ray diagram can be used to determine the position and size of an image

They are graphical constructions which tell the overall nature of the image

They can also be used to check the parameters calculated from the mirror and magnification equations

Drawing A Ray Diagram

To make the ray diagram, you need to know The position of the object The position of the center of curvature

Three rays are drawn They all start from the same position on the object

The intersection of any two of the rays at a point locates the image The third ray serves as a check of the construction

The Rays in a Ray Diagram

Ray 1 is drawn parallel to the principle axis and is reflected back through the focal point, F

Ray 2 is drawn through the focal point and is reflected parallel to the principle axis

Ray 3 is drawn through the center of curvature and is reflected back on itself

1

3

2

Notes About the Rays

The rays actually go in all directions from the object

The three rays were chosen for their ease of construction

The image point obtained by the ray diagram must agree with the value of q calculated from the mirror equation

Concave Mirror:object is beyond focal point


Concave: Object located at Center of Curvature

http://www.glenbrook.k12.il.us/gbssci/Phys/mmedia/optics/rdcmb.html

Object is between focal point & mirror


Ray Diagrams

A ray diagram may help one determine the approximate location and size of the image, it will not provide numerical information about image distance and object size.

The mirror equation expresses the quantitative relationship between the object distance (do), the image distance (di), and the focal length (f).

Magnification equation relates the ratio of the image distance and object distance to the ratio of the image height (hi) and object

height (ho).

Ray Diagram for Concave Mirror, do > R

The image is real The image is inverted The image is smaller than the object

Ray Diagram for a Concave Mirror, do < f

The image is virtual The image is upright The image is larger than the object

Ray Diagram for a Convex Mirror

The image is virtual The image is upright The image is smaller than the object

Notes on Images With a concave mirror, the image may be either

real or virtual When the object is outside the focal point, the image is

real When the object is at the focal point, the image is

infinitely far away (to the left in the previous diagrams) When the object is between the mirror and the focal

point, the image is virtual With a convex mirror, the image is always virtual

and upright As the object distance increases, the virtual image gets

smaller

Practice A convex mirror has a focal length of -10.8

cm. An object is placed 32.7 cm from the mirror's surface. Determine the image distance.

di = 8.1 cm

Determine the focal length of a convex mirror which produces an image which is 16.0 cm behind the mirror when the object is 28.5 cm from the mirror.

f = 36.6 cm

Drawing Ray Diagrams (to determine where an image appears)

Law of Reflection applies 1. incident ray: drawn parallel to axis reflects:

through focal point 2. incident ray: drawn through center (C)

reflects: back through center of curvature

3. incident ray: passes through (or appears to) focal point reflects: parallel to axis.

Concave mirror with object beyond focal pointStart from the top

of the object, travel parallel to the

principle axis and aim for the mirror

Start from the top of the object, travel

parallel to the principle axis and aim for the mirror

Reflect through the focal point


Start from the top of the object, pass through the focal point and aim for

the mirror

Start from the top of the object, pass through the focal point and aim for

the mirror

Reflect parallel to the the

principle axis

Reflect parallel to the the

principle axis

A REAL image forms where the reflected

rays intersect

A REAL image forms where the reflected

rays intersect

Image formed is:Real

InvertedReduced

Image formed is:Real

InvertedReduced

Image between Focal Point and Mirror

As you can see, the reflected rays do not cross. That

means that no REAL image forms

As you can see, the reflected rays do not cross. That

means that no REAL image forms

Concave Mirror with object between focal point and mirror

Start from the top of the object,

guide from the focal point and

aim for the mirror



aim for the mirror

Reflect parallel to the principle

axis

Reflect parallel to the principle

axis







Extend virtual lines behind the mirror from the reflected

rays.

Extend virtual lines behind the mirror from the reflected

rays.A VIRTUAL image forms

where the virtual rays

intersect

A VIRTUAL image forms


intersect

Image formed is:VirtualUpright

Enlarged


Enlarged

Object in front of focal point of Concave Mirror


Concave mirror with object at focal point




parallel to the principle axis and aim for the mirrorReflect

through the focal point


The normal second ray cannot be drawn because

you cannot go through the focal point and still hit

the mirror

The normal second ray cannot be drawn because

you cannot go through the focal point and still hit

the mirror

Start from the top of the object and aim for the point

where the principle axis

meets the mirror

Start from the top of the object and aim for the point

where the principle axis

meets the mirror

The reflected ray follows the Law of reflection with an angle equal to the angle of incidence

The reflected ray follows the Law of reflection with an angle equal to the angle of incidence

The reflected rays will

never cross because they are parallel

The reflected rays will

never cross because they are parallel

No image formed:Results in a

complete blur

No image formed:Results in a

complete blur

Convex Mirror (diverging)

Forms virtual, upright, and smaller image

Reflected light rays never meet so they cannot produce a real image

Convex Mirror

Convex Mirror





Reflect using the focal point as a guide. The red is reflected light

and the dashed green is the virtual ray that passes through the

focal point.

Reflect using the focal point as a guide. The red is reflected light

and the dashed green is the virtual ray that passes through the

focal point.



aim for the mirror



aim for the mirrorReflect parallel to the the principle axis and draw the virtual ray behind the mirror

Reflect parallel to the the principle axis and draw the virtual ray behind the mirror



intersect



intersect


Reduced


Reduced

Documents

Color Deficiency. Why do we see certain colors? We perceive only the reflected colors