Chapter 16 “Fundamentals of Light” Glencoe Physics Chapter 16 “Fundamentals of Light”

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

The Electromagnetic Spectrum cosmic high frequency short wavelength gamma x ray ultraviolet visible infrared microwaves radio waves electricity low frequency long wavelength

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

Speed of Light Light moves at a speed of over 186,000 miles per second or 3 X 108m/s. If a gun fired a bullet that moved at this speed, how many trips could it make around the world in one second? c = f  The AM radio band extends from 5.4 X 105 Hz to 1.7 X 106 Hz. What are the longest and shortest wavelengths in this frequency range?

Illumination of a Point Source Light obeys the inverse square law. If light is emitted from a point source having an intensity of one candle, at a distance of 1m, the intensity would be ___ lumen. At a distance of 2m, the intensity would be ___ lumens. The equation relating light intensity and distance would be, I - intensity in cd E = I / d2 E - illumination in lm d - distance in m P438,8-12

Flat Mirrors Regular reflection enables us to see images of objects in mirrors. Light rays reflect from objects and fall on mirrors and are reflected in all directions. This enables us to see an image of the object in infinite locations. A plane mirror reflects light rays in the same manner that they approach it.

Reflection of Light Reflection of light involves the return of light waves from an opaque object. This property enables us to see objects. Law of Reflection The angle of incidence is equal to the angle of reflection. regular reflection - parallel incident rays are reflected parallel irregular reflection - parallel incident rays are reflected nonparallel

The image in a plane mirror is; 1. upright - not upside down 2. reversed left to right - reflections of others are reversed 3. the same size - no enlargement or reduction 4. located the same distance behind the mirror as the object is in front of the mirror - image gets smaller as you move away 5. virtual - not real, appears to be behind the mirror Page 463; 6,9,10

Curved Mirrors Converging mirrors are also referred to as concave mirrors. They may be thought of as an infinite number of plane mirrors located along a curved path. The images seen in concave mirrors depends on the relative distance between the mirror and the object. There are six different cases of which images can be generally defined. To determine these cases, one must be able to draw an optic diagram which can be used to locate the image.

Draw a concave mirror and label the following parts. F - focal point f - focal length C - center of curvature r- radius of curvature di - distance to image do- distance to object V - vertex --------------------------------------------------------axis

Mathematical Relationships 1. radius of curvature - r, focal length - f r = 2f 2. distance to object - do, distance to image - di, focal length - f 1/f = 1/di + 1/do 3. size of object - so, size of image - si, distance to object - do, distance to image di si/so = di/do

Sample Problems 1. A concave mirror has a focal length of 20cm. Find the radius of curvature of the mirror. 2. An object is located 36cm from a concave mirror having a radius of curvature of 24cm. Locate the image. 3. The object in problem #2 is 3cm tall. Find the height of the image.

Six Cases of Images Formed in Converging Mirrors 1. Object at infinity, Image is.......... ---------------------------------------------------------axis

Six Cases of Images Formed in Converging Mirrors 2. Object beyond C, Image is.......... ---------------------------------------------------------axis

Six Cases of Images Formed in Converging Mirrors 3. Object at C, Image is.......... ---------------------------------------------------------axis

Six Cases of Images Formed in Converging Mirrors 4. Object between C & F, Image is.......... ---------------------------------------------------------axis

Six Cases of Images Formed in Converging Mirrors 5. Object at F, Image is.......... ---------------------------------------------------------axis

Six Cases of Images Formed in Converging Mirrors 6. Object between F & V, Image is.......... ---------------------------------------------------------axis Assignment: Page 469; 12-16

Virtual Images Formed by Convex Mirrors Certain mirrors cause reflected rays to diverge or propagate in such a manner that they never cross. Another name given to this type of diverging mirror is a "convex" mirror. Uses of diverging mirrors include... 1. rear view mirrors 2. supermarket isle mirrors

Draw a diagram of an object located in front of a diverging mirror. --------------------------------------------------------axis Image is....

Sample Problem An object is located 20cm from a diverging mirror of 8cm focal length. Locate the image. The object is 4cm tall. How tall is the image? Assignment: Page 472; 17-21

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

Polarization of Light → →

Polarization Photography Reduce Sun Glare Reduce Reflections Darkens Sky Increase Color Saturation Reduce Haze 25

Polarization Photography Without Polarizer With Polarizer Provides better Color Saturation Darkens the sky 26

Polarization Photography Without Polarizer With Polarizer 27

Polarization Photography : Scattering Haze De-hazed 28

Polarization Photography : Wide Angle Lenses Vignetting of the Sky 29

Polarization Photography : Reflections Reduce Reflections 30

Polarization Photography : Reflections Reduce Reflections 31

Polarization Photography : Reflections Many titled planes 32

Aqua-polaricam 33

Polarization Photography : Underwater Offshore structures Offshore drilling rigs Vessel inspection Underwater ROV/AOV Marine biology Recreational photography Marine archaeology Underwater pipelines and communication Underwater mapping 34

Birefrengence Interference pattern due to different refractive indices 35

Light as Plane Waves Sinusoidal plane waves very good approximation. 180 o 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. 36

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. 37

Linear Polarization 38

Circular Polarization 39

Elliptical Polarization 40

Crossed Polarizers 41

Polarizer Puzzle If crossed polarizers block all light, why does putting a third polarizer at 45° between them result in some transmission of light? 42

Law of Malus Amplitude: Intensity = Const . (Amplitude)^2 43

Polarized Sunglasses Reduce glare off the roads while driving 44

Frequently Asked Questions Why is a red shirt red? Most of us know that red shirts are red because they reflect red light and absorb other frequencies. Why is black clothing warmer that white clothing? Black absorbs all frequencies. Why do cars get hot in the summer when the windows are rolled up? Visible light passes through the glass and strikes the interior which interferes with the frequencies and converts the light to infrared, heat, which will not pass through the glass.