Chapters 14 and 15 OPTICS

 c is the speed of light = 3.00 x 10 8 m/s this is the value for light in space or our atmosphere.  speed = (wavelength) x (frequency)  c = ƒ

 AM Radio waves  7.4 x 10 5 Hz = ?

 E = ħf  E is energy  ħ is Planks constant, depending on units it can either be 6.626x10 −34 Js (Joules seconds) or 4.14×10 −15 eVs (electronvolt seconds)  f is frequency

 Magnetic field wave perpendicular to an electric field wave  All objects emit EMWs.   Temp  EMW  Electromagnetic spectrum  Range of all frequencies of light  Visible light is a very small portion of that entire spectrum.

 Low energy waves with long wavelengths  Includes FM, AM, radar and TV waves  Wavelengths of m and longer  Low frequency  Used in many devices such as remote control items, cell phones, wireless devices, etc. The Electromagnetic Spectrum8

 Shorter than radio, longer than light and infrared  Wavelength 1 x m to 1 x m  First used in radar, now used in communication, medicine, and consumer use (microwave ovens) The Electromagnetic Spectrum9

10  Invisible electromagnetic waves that are detected as heat  Can be detected with special devices such as night goggles  Used in heat lamps, ac/heating industry  Higher energy than microwaves but lower than visible light  Can be used to detect poor insulation in houses.

The Electromagnetic Spectrum11

 The portion of the electromagnetic spectrum that human eyes can detect  ROY G BIV (red, orange, yellow, green, blue, indigo, violet)  Red is the lowest frequency and violet is the highest frequency  Usually reported in nanometers (10 -9 m) The Electromagnetic Spectrum12

The Electromagnetic Spectrum13

 Higher energy than light waves  Can cause skin cancer and blindness in humans  Used in tanning beds and sterilizing equipment The Electromagnetic Spectrum14

 High energy waves!  Used in medicine, industry and astronomy  Can cause cancer if you get more than a few dozen per year, depending on where you’re getting the imaging on your body.  That was my thumb last spring break…. The Electromagnetic Spectrum15

 Highest energy, generated by nuclear explosions in stars  Blocked from Earth’s surface by atmosphere  Used in cancer therapy since they kill cells  Gamma-ray bursts from outside our galaxy can release more energy in 10 seconds than the Sun will emit in its entire 10 billion-year lifetime! The Electromagnetic Spectrum16

 Light waves travel in straight paths  Change in substance changes direction  Opaque - does not permit light  some light reflected  some light absorbed as heat  Translucent- does permit some light  Transparent- all light goes through

 Texture affects reflection  Diffuse reflection ( rough)  reflects light in many different directions,  Specular reflection ( smooth)  reflects light in only one direction  Smooth – variations in surface 

Specular and Diffuse Reflection Specular Diffuse

 Substances that are transparent or translucent allow light to pass through them.  Changes direction of light, bends the light  Due to the differences in speed of light

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

 Light may refract into a material where its speed is higher  The angle of refraction is greater than the angle of incidence  The ray bends away from the normal

 The ratio of the speed of light in a vacuum to the speed of light in a medium   n -  c

 Ray  is the incident ray  Ray  is the reflected ray  Ray is refracted into the lucite  Ray  is internally reflected in the lucite  Ray is refracted as it enters the air from the lucite

 The index of refraction defines the velocity of light in the optically denser medium v= c/n. Speed of light in vacuum (air) Speed of light in a medium (e.g. water) Index of refraction

 For a vacuum, n = 1  For any other media, n > 1  n is a unitless ratio

SubstanceRefractive index Air Water1.33 Ethyl alcohol1.36 Fused quartz1.46 Glycerine1.47 Glass Oil1.50 Zircon1.92 Diamond2.42 Some indices of refraction for various substances at 590 nm:

 As light travels from one medium to another, its frequency does not change  Both the wave speed and the wavelength do change  The wavefronts do not pile up, nor are created or destroyed at the boundary, so ƒ must stay the same

 n 1 (sin  1 ) = n 2 (sin  2 )  To solve for an angle, take inverse sine   r = sin -1 {(n 1/ n 2 )(sin  1 )}  Example   1 = 30.0 ⁰  n 1 = 1.00  n 2 = 1.52

 i = 30.0 ⁰ n 1 = 1.00 n 2 = 1.52  r = ? Sometimes they have i Instead of 1 and r instead of 2!

 If the angle of incidence of a ray is greater than a certain critical angle the ray will reflect rather than refract- it won’t escape the medium!  This principal is responsible for the properties of fiber optic cables.

 sin Θ c = n 2 / n 1  When solving, Θ c = sin -1 (n 2 / n 1 )  What is the critical angle for light traveling from Diamond to Air? n diamond = 2.42, n air =1.00

 Light striking a mirror reflects at the same angle that it struck the mirror. Angle in equals angle out.

 s i = s o  s i : objects distance to the mirror  s o : distance from the mirror to the image  f : focal point  All flat mirrors create a virtual image  Does not exist  Made by our eyes  Behind mirror- that means virtual!

q p You Your image

 Used to predict the location of the image of an object. Usually shown as red lines. p q

 Reflective surface is on the interior of a curved surface  C – center of curvature = 2f  R – Radius (distance to C)  f – Focal Point (1/2 R)-or- commonly written as f=R/2. See this in the picture at top of page 503.  Principal axis  any line that passes through C (point where R goes out to) and the middle of the mirror

 1/object distance + 1/image distance = 1/focal length 1/ s i + 1/s 0 = 1/ f  Magnification (M) Image height/object height or M= ( h i / h o ) -Image distance/Object distance M = - (s i / s o )

Sign of MOrientation of ImageType of Image + UprightVirtual – InvertedReal

 A ray traveling through C will reflect back through C  A ray traveling through (f) will reflect parallel to the PA  A 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

 Reflective surface is on the outside of the curve.  The points f and C are located behind the mirror!

 A ray parallel to the PA will reflect directly away from f.  A ray towards f will reflect parallel to the PA  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

 f = -8.00cm  p = 10.0cm  h = 3cm

 Rays 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.

 Converging  Diverging  f- curve of lens & index of refraction

1. Ray parallel to PA, refracts through far focal point 2. Ray through center of lens, continues straight line 3. Ray through near focal point, refracts through lens, continues parallel to PA  Treat lens as though it were a flat plane.

 Because 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 PA  Ray 3 - ray through center, continues straight, trace back toward object

Sign pqF + Near side of lens Far side of lens Convergin g Lens – Far side of lens Near side of lens Diverging Lens

 p = 30.0cm  f = 10.cm

 p = 12.5cm  f = -10.0cm