Light, Reflection, and RefractionChapters 14 and 15OPTICS

Electromagnetic WavesMagnetic field wave perpendicular to an electric field wave

All objects emit EMWs. Temp EMWElectromagnetic spectrum Range of all frequencies of lightVisible light is a very small portion of that entire spectrum.

cSpeed of Light - 3.00 x 108m/s.

= (wavelength) x (frequency)

c =

ExampleAM Radio waves 5.4 x 105 Hz1.7 x 106 Hz = ?

Visible LightPart of the EMS humans can seeRed - 750nm (x10-9m) Purple - 380nmBees, Birds UVSnakes IR

ReflectionLight waves usually travel in straight pathsChange in substance changes directionOpaque - does not permit lightsome light reflectedsome light absorbed as heat

ReflectionTexture affects reflectionDiffuse reflection (rough) reflects light in many different directions, Specular reflection (smooth)reflects light in only one directionSmooth variations in surface

MirrorsLight striking a mirror reflects at the same angle that it struck the mirror

Flat Mirrorsp = qp- objects distance to the mirrorq - distance from the mirror to the imageVirtual imageDoes not existMade by our eyes

Ray DiagramsUsed to predict the location of the image of an object

Concave Spherical MirrorsReflective surface is on the interior of a curved surface C center of curvatureR Radius (distance to C)f Focal Point (1/2 R)Principal axisany line that passes through C usually oriented with an object

Mirror Equations1/object distance + 1/image distance = 1/focal length1/p + 1/q = 1/fMagnification (M) = Image height/object height (h / h) - (q / p)M = h / h = - (q / p)

Sign of Magnification

Sign of MOrientation of ImageType of Image+UprightVirtual InvertedReal

Concave Spherical Mirror RulesA ray traveling through C will reflect back through CA ray traveling through (f) will reflect parallel to the PAA ray traveling to the intersection of the PA and the mirror will reflect at the same angle below the PA.A ray traveling parallel to PA will reflect through the focal point

Ray DiagramsDraw three raysThe image forms at the point of intersectionExamplef = 10.0cmp = 30.0cmh = 3.00cm

Convex Spherical MirrorsReflective surface is on the outside of the curve. The points f and C are located behind the mirrornegative

RulesA ray parallel to the PA will reflect directly away from f.A ray towards f will reflect parallel to the PAA ray towards C will reflect directly away from C.A ray to the intersection of PA and mirror will reflect at the same angle below the OA.Trace the 3 diverging lines back through the mirror to reveal the location of the image which is always virtual

Examplef = -8.00cmp= 10.0cmh = 3cm

Parabolic MirrorsRays that hit spherical mirrors far away from the OA often reflect though other points causing fuzzy images, spherical aberration.Telescopes use parabolic mirrors as they ALWAYS focus the rays to a single point.

RefractionSubstances that are transparent or translucent allow light to pass though them. Changes direction of light Due to the differences in speed of light

AnalogyA good analogy for refracting light is a lawnmower traveling from the sidewalk onto mud

Index of Refraction (n)The ratio of the speed of light in a vacuum to the speed of light in a medium

n - c

Snells Lawni(sini) = nr(sinr) r = sin-1{(ni/ nr)(sini)}Examplei = 30.0ni = 1.00nr = 1.52

i = 30.0ni = 1.00nr = 1.52

Total Internal ReflectionIf the angle of incidence of a ray is greater than a certain critical angle the ray will reflect rather than reflect This principal is responsible for the properties of fiber optic cables.Remember the lawn mower analogy

Critical Anglesin c = nr / niAs long as nr < ni

What is the critical angle for light traveling from Diamond to Air?

nr = 1.000 ni = 2.419

Thin LensesConverging

Diverging

f- curve of lens & index of refraction

Converging Lens DiagramRay parallel to PA, refracts through far focal pointRay through center of lens, continues straight lineRay through near focal point, refracts through lens, continues parallel to PA

Treat lens as though it were a flat plane.

Diverging Lens DiagramBecause the rays that enter a diverging lens do not intersect a virtual image is formed by tracing back the refracted rays.Ray 1 - parallel to PA, refracts away from near f, trace back to near f.Ray 2 - ray toward far f, refracts parallel to PA, trace back parallel to PARay 3 - ray through center, continues straight, trace back toward object

Sign Conventions for Lens

SignpqF+Near side of lensFar side of lensConverging Lens Far side of lensNear side of lensDiverging Lens

Converging Lens Example p = 30.0cmf = 10.cm

Diverging Lens Example p = 12.5cmf = -10.0cm

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