Light. E.M. waves electromagnetic both electric and magnetic characteristics travels at 3.0 x 10 8 m/s in a vacuum slower in material mediums

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1 Light E.M. waves electromagnetic both electric and magnetic characteristics travels at 3.0 x 10 8 m/s in a vacuum slower in material mediums 1) requires no medium but can travel through them 2) is energy transferred in wave motion the energy is in packets called quanta or photons 3) E.M. waves are produced by oscillations of electrons capa.org/~mmp/applist/spectrum/s.htm spectrum astr.gsu.edu/hbase/hframe.html use with spectrum wave/particle May 18 8:17 AM 1

2 elect/mag fields oscil particle use Java on Polarization and Brewster angle May 21 2:52 PM 2

3 energy is absorbed by electrons (excited) by electricity, heat, light, or chemicals energy is given off by the electron as a photon (quanta). The energy of the photon shows up as different frequencies of EM waves the higher the energy the higher the frequency. May 18 8:52 AM 3

4 May 19 7:11 AM 4

5 May 19 7:11 AM 5

6 dual nature of light "wavicle" an'allen'ism LIGHT packets of energy (photon, quanta) traveling in wave form May 19 7:46 AM 6

7 Measuring the speed of light ed_evidence.html Roemer's discovery 3.htm May 19 8:48 AM 7

8 Ole Roemer 1670's r eo time difference of 16 minutes r eo = 1.5 x m orbital diameter is 3.0 x m it took 16 minutes for light to translate the earth's orbital diameter v = d/t v = 3.0 x m/960 s = 3.15 x 10 8 m/s May 18 7:26 AM 8

9 Light from the source passes through a narrow slit. It is reflected by face A of the octagonal metal prism. It then travels a distance, s, (a few kilometres) and returns to be reflected by face B. The prism now rotates. If it rotates fast enough, when light returns to the prism, face B is no longer in the right position to reflect it into the observer s eye. The image of the slit disappears. The speed of rotation is increased. At a certain speed of rotation, the image of the slit reappears. This is because the time taken for light to go from face A to face B was the same as the time taken by the prism to rotate 1/8 th of a revolution. If the prism completes n rotations per second then the time for one revolution is 1/n. Therefore, the time taken for the light to cover the distance, s is given by use this May 18 7:35 AM 9

10 @530 rps Mt Wilson is about 22.5 miles from Mt San Antonio f = 530 rev/s T = /8 T = v = 45 miles(1610 m/mile)/ s v = 3 x 10 8 m/s May 18 7:41 AM 10

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12 Inverse Square Law Illumination (E) on a surface varies inversely with the square of the distance from the source. E = 1/r 2 May 23 6:43 AM 12

13 May 23 6:46 AM 13

14 luminous flux (P): rate visible light is emitted from a source in all directions measured in lumens (lm) ex. 100 W light 1750 lm note this is all the light that is emitted from a source! illuminance (E): illumination of a surface rate light falls on a surface measured in lux... lm/m 2 E = P/A = P/4πr 2 ex. source is 100W = 1750 lm surface is 1 m away E = 1750 lm/4π(1m) 2 = 140 lx surface 2 m away E = 1750 lm/4π(2m) 2 = 35 lx lumiinous intensity (I): the luminous flux that falls on a 1m 2 surface measured in "candela" cd "I" rates a source luminous flux divided by 4π I = P/4π May 19 8:53 AM 14

15 luminous flux (P): rate visible light is emitted from a source in all directions measured in lumens (lm) ex. 100 W light 1750 lm note this is all the light that is emitted from a source! Luminous flux is photometrically weighted radiant flux (power). The luminous flux is a very basic unit of measurement for light. If a uniform point light source of 1 cd luminous intensity (about the intensity of a normal wax candle!) is positioned at the center of a sphere of 1 m radius, then every area of 1 m 2 on the inside of that sphere will receive a luminous flux of 1 lm. Since the surface area of a full sphere is 4πr 2, a uniform point light source of 1 cd produces a total lm of luminous flux. May 19 10:19 AM 15

16 luminous intensity (I): the luminous flux that falls on a 1m 2 surface measured in "candela" cd luminous flux divided by 4 π I = P/4π The luminous intensity is the luminous flux emitted from a point per unit solid angle in a particular direction. The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x hertz and that has a radiant intensity in that direction of 1/683 watt per steradian. May 19 10:14 AM 16

17 A 52 watt bulb emits 700 lm of light. What is the illumination of a surface 1.5 m below it? b) What is the intensity of the light? E =? P = 700 lm r = 1.5 m I =? luminous flux in lumens intensity is in candelas E = P/4πr 2 E = 700 lm/4π(1.5 m) 2 E = 24.8 lm/m 2 I = P/4π I = 700 lm/4π I = 56 cd May 19 10:30 AM 17

18 May 13 11:08 AM 18

19 Color addition: Light combining to form white light Red, green, and blue are the primary colors for addition red Magenta, cyan, and yellow are the secondary colors for color addition yellow magenta red and blue make magenta green cyan blue blue and green make cyan green and red make yellow capa.org/~mmp/applist/rgbcolor/c.htm May 21 7:27 AM 19

20 Color subtraction: color produced by selective absorption and reflection. (dyes and pigment) primary pigments absorb one primary color and reflect two. primary pigments yellow absorbs blue and reflects red and green cyan absorbs red and reflects blue and green magenta absorbs green and reflects red and blue secondary pigements absorb two primary colors and reflect one. verizon.net/vz eoacw1/colors ub.html secondary pigments red absorbs green and blue and reflects red green absorbs red and blue and reflects green blue absorbs green and red reflects blue Note that the primary pigments are the same as the secondary light colors, and the secondary pigments arfe the same as the primary light colors capa.org/~mmp/applist/cymcolor/c.htm May 21 7:27 AM 20

21 thin film When light strikes a thin film the boundary is fixed and the light is reflected inverted. The transmited light is bent slightly (refracted) and strikes the second surface which is an open boundary and reflected with no change in phase. It now returns to the first surface and transmits into the original medium. When the thickness of the film obeys the 1/4 λ rule the two waves superposition with constructive interference and becomes more intense (bright). Each wavelength of light requires a difference thickness of film for constructive interference. May 21 7:44 AM 21

22 May 22 12:58 PM 22

23 May 21 3:00 PM 23

24 May 21 2:53 PM 24

25 lens prism/rainbow rainbow adv physics black body radiation May 14 12:13 PM 25

26 The speed of light depends on the medium 2.25 x 10 8 m/s 2.0 x 10 8 m/s 1.25 x 10 8 m/s May 16 7:04 AM 26

27 The electromagnetic Spectrum May 19 7:10 AM 27

28 May 13 8:53 AM 28

29 Attachments lens.ppt