Glencoe PhysicsGlencoe Physics

Chapter 16Chapter 16

““Fundamentals of Light”Fundamentals of Light”

Characteristics of Light

From our knowledge of waves, we know they vary From our knowledge of waves, we know they vary in frequency and wavelength. We have also in frequency and wavelength. We have also determined that light has wave and particle determined that light has wave and particle properties. Light is probably our most important properties. Light is probably our most important means of learning about the physical nature of our means of learning about the physical nature of our universe.universe.

light - that portion of the electromagnetic spectrum light - that portion of the electromagnetic spectrum that stimulates the human eyethat stimulates the human eye

The Electromagnetic Spectrum cosmiccosmic high frequency high frequency short wavelengthshort wavelength gammagamma x rayx ray ultravioletultraviolet visiblevisible infraredinfrared microwavesmicrowaves radio wavesradio waves electricity low frequencyelectricity low frequency long wavelengthlong wavelength

Optical Terms

luminous body - an object which emits its own light luminous body - an object which emits its own light Example (sun)Example (sun) illuminous body - an object which reflects light illuminous body - an object which reflects light Example (moon)Example (moon) transparent object - allows total light transmissiontransparent object - allows total light transmission Example (glass)Example (glass) translucent object - allows partial transmissiontranslucent object - allows partial transmission Example (church window)Example (church window) opaque object - does not allow light transmission opaque object - does not allow light transmission Example (wall)Example (wall)

Speed of LightSpeed of Light Light moves at a speed of over 186,000 miles per Light moves at a speed of over 186,000 miles per

second or 3 X 10second or 3 X 1088m/s.m/s. If a gun fired a bullet that moved at this speed, how If a gun fired a bullet that moved at this speed, how

many trips could it make around the world in one many trips could it make around the world in one second?second?

c = c = f f The AM radio band extends from 5.4 X 10The AM radio band extends from 5.4 X 1055 Hz to 1.7 Hz to 1.7

X 10X 1066 Hz. What are the longest and shortest Hz. What are the longest and shortest wavelengths in this frequency range?wavelengths in this frequency range?

Illumination of a Point Source Light obeys the inverse square law. If light is emitted Light obeys the inverse square law. If light is emitted

from a point source having an intensity of one candle, from a point source having an intensity of one candle, at a distance of 1m, the intensity would be ___ lumen. at a distance of 1m, the intensity would be ___ lumen. At a distance of 2m, the intensity would be ___ At a distance of 2m, the intensity would be ___ lumens. The equation relating light intensity and lumens. The equation relating light intensity and distance would be,distance would be,

I - intensity in cdI - intensity in cd E = I / dE = I / d22 E - illumination in lmE - illumination in lm d - distance in md - distance in m P438,8-12P438,8-12

Flat Mirrors

Regular reflection enables us to see images of objects Regular reflection enables us to see images of objects in mirrors. in mirrors.

Light rays reflect from objects and fall on mirrors Light rays reflect from objects and fall on mirrors and are reflected in all directions. and are reflected in all directions.

This enables us to see an image of the object in This enables us to see an image of the object in infinite locations. infinite locations.

A plane mirror reflects light rays in the same manner A plane mirror reflects light rays in the same manner that they approach it.that they approach it.

Reflection of Light Reflection of light involves the return of light waves Reflection of light involves the return of light waves

from an opaque object. This property enables us to from an opaque object. This property enables us to see objects.see objects.

Law of ReflectionLaw of Reflection The angle of incidence is equal to the angle of The angle of incidence is equal to the angle of

reflection.reflection. regular reflection - parallel incident rays are regular reflection - parallel incident rays are

reflected parallelreflected parallel irregular reflection - parallel incident rays are irregular reflection - parallel incident rays are

reflected nonparallelreflected nonparallel

The image in a plane mirror is; 1. upright - not upside down1. upright - not upside down 2. reversed left to right - reflections of others are 2. reversed left to right - reflections of others are

reversedreversed 3. the same size - no enlargement or reduction3. the same size - no enlargement or reduction 4. located the same distance behind the mirror as the 4. located the same distance behind the mirror as the

object is in front of the mirror - image gets smaller as object is in front of the mirror - image gets smaller as you move awayyou move away

5. virtual - not real, appears to be behind the mirror5. virtual - not real, appears to be behind the mirror Page 463; 6,9,10Page 463; 6,9,10

Curved Mirrors Converging mirrors are also referred to as concave Converging mirrors are also referred to as concave

mirrors. mirrors. They may be thought of as an infinite number of plane They may be thought of as an infinite number of plane

mirrors located along a curved path.mirrors located along a curved path. The images seen in concave mirrors depends on the The images seen in concave mirrors depends on the

relative distance between the mirror and the object. relative distance between the mirror and the object. There are six different cases of which images can be There are six different cases of which images can be

generally defined. generally defined. To determine these cases, one must be able to draw an To determine these cases, one must be able to draw an

optic diagram which can be used to locate the image.optic diagram which can be used to locate the image.

F - focal pointF - focal point f - focal length f - focal length C - center of curvature r- radius of curvatureC - center of curvature r- radius of curvature di - distance to image do- distance to object di - distance to image do- distance to object V - vertexV - vertex

--------------------------------------------------------axis--------------------------------------------------------axis

Draw a concave mirror and label the following parts.

Mathematical Relationships 1. radius of curvature - r, focal length - f 1. radius of curvature - r, focal length - f

r = 2fr = 2f

2. distance to object - do, distance to image - di, 2. distance to object - do, distance to image - di, focal length - ffocal length - f

1/f = 1/di + 1/do1/f = 1/di + 1/do 3. size of object - so, size of image - si, distance 3. size of object - so, size of image - si, distance

to object - do, distance to image dito object - do, distance to image di si/so = di/dosi/so = di/do

Sample Problems 1. A concave mirror has a focal length of 20cm. 1. A concave mirror has a focal length of 20cm.

Find the radius of curvature of the mirror. Find the radius of curvature of the mirror. 2. An object is located 36cm from a concave 2. An object is located 36cm from a concave

mirror having a radius of curvature of 24cm. mirror having a radius of curvature of 24cm. Locate the image.Locate the image.

3. The object in problem #2 is 3cm tall. Find 3. The object in problem #2 is 3cm tall. Find the height of the image.the height of the image.

Six Cases of Images Formed in Converging Mirrors

1. Object at infinity, Image is..........1. Object at infinity, Image is..........

---------------------------------------------------------axis---------------------------------------------------------axis

Six Cases of Images Formed in Converging Mirrors

2. Object beyond C, Image is..........2. Object beyond C, Image is..........

---------------------------------------------------------axis---------------------------------------------------------axis

Six Cases of Images Formed in Converging Mirrors

3. Object at C, Image is..........3. Object at C, Image is..........

---------------------------------------------------------axis---------------------------------------------------------axis

Six Cases of Images Formed in Converging Mirrors

4. Object between C & F, Image is..........4. Object between C & F, Image is..........

---------------------------------------------------------axis---------------------------------------------------------axis

Six Cases of Images Formed in Converging Mirrors

5. Object at F, Image is..........5. Object at F, Image is..........

---------------------------------------------------------axis---------------------------------------------------------axis

Six Cases of Images Formed in Converging Mirrors

6. Object between F & V, Image is..........6. Object between F & V, Image is..........

---------------------------------------------------------axis---------------------------------------------------------axis

Assignment: Page 469; 12-16Assignment: Page 469; 12-16

Virtual Images Formed by Convex Mirrors

Certain mirrors cause reflected rays to diverge Certain mirrors cause reflected rays to diverge or propagate in such a manner that they never or propagate in such a manner that they never cross. cross.

Another name given to this type of diverging Another name given to this type of diverging mirror is a "convex" mirror. mirror is a "convex" mirror.

Uses of diverging mirrors include...Uses of diverging mirrors include... 1. rear view mirrors1. rear view mirrors 2. supermarket isle mirrors2. supermarket isle mirrors

Draw a diagram of an object located in front of a diverging mirror.

--------------------------------------------------------axis--------------------------------------------------------axis

Image is....Image is....

Sample Problem

An object is located 20cm from a An object is located 20cm from a diverging mirror of 8cm focal length. diverging mirror of 8cm focal length. Locate the image.Locate the image.

The object is 4cm tall. How tall is the The object is 4cm tall. How tall is the image?image?

Assignment: Page 472; 17-21Assignment: Page 472; 17-21

Color and Polarization

Color is a property of light which is a Color is a property of light which is a result of varying frequency. The result of varying frequency. The wavelength is also used to distinguish wavelength is also used to distinguish colors. The range of visible light for colors. The range of visible light for wavelength is 400nm for violet to wavelength is 400nm for violet to 700nm for red.700nm for red.

Polarization of LightPolarization of Light→→

Polarization Photography

Reduce Sun GlareReduce ReflectionsDarkens SkyIncrease Color SaturationReduce Haze

Polarization Photography

Without Polarizer With Polarizer

• Provides better Color Saturation

• Darkens the sky

Polarization Photography

Without Polarizer With Polarizer

Polarization Photography : Scattering

De-hazedHaze

Polarization Photography : Wide Angle Lenses

Vignetting of the Sky

Polarization Photography : Reflections

Reduce Reflections

Polarization Photography : Reflections

Reduce Reflections

Polarization Photography : Reflections

Many titled planes

Aqua-polaricamAqua-polaricam

Polarization Photography : Underwater

• Underwater pipelines and communication

• Offshore structures

• Underwater ROV/AOV

• Offshore drilling rigs

• Vessel inspection

• Recreational photography

• Marine archaeology

• Marine biology

• Underwater mapping

Birefrengence

Interference pattern due to different refractive indices

Light as Plane Waves

•Sinusoidal plane waves very good approximation.

•Very useful for characterizing polarization.

•Polarized Wave: Has only one preferred orientation.

•Un-polarized Wave: Has no preferred orientation. or has all orientations.

•Partially polarized wave: Has preferred orientation but has energy in other orientations as well.

180o

minI

maxI

max

Classification of Polarization

Linear : Two orthogonal plane waves with same phase but possibly different amplitudes.

Circular: Two orthogonal plane waves with 90 deg phase shift but same amplitudes.

Elliptical: Possibly any degree phase shift with different amplitudes.

Linear Polarization

Circular Polarization

Elliptical Polarization

Crossed Polarizers

Polarizer Puzzle

If crossed polarizers block all light, why does putting a third polarizer at 45° between them result in some transmission of light?

Law of Malus

Amplitude:

Intensity = Const . (Amplitude)^2

Polarized Sunglasses

Reduce glare off the roads while driving

Frequently Asked Questions Why is a red shirt red? Why is a red shirt red? Most of us know that red shirts are red because they Most of us know that red shirts are red because they

reflect red light and absorb other frequencies. reflect red light and absorb other frequencies. Why is black clothing warmer that white clothing?Why is black clothing warmer that white clothing? Black absorbs all frequencies.Black absorbs all frequencies. Why do cars get hot in the summer when the windows Why do cars get hot in the summer when the windows

are rolled up?are rolled up? Visible light passes through the glass and strikes the Visible light passes through the glass and strikes the

interior which interferes with the frequencies and interior which interferes with the frequencies and converts the light to infrared, heat, which will not pass converts the light to infrared, heat, which will not pass through the glass.through the glass.