PowerPoint PresentationSlide 2Alternate Exam TimeProperties of wavesCh 22, 21.5-7: Waves & interferencePhase difference & interferenceQuestionTwo-slit interferenceTwo-slit interference: path lengthReflection phase shiftThin film interferenceThin-film interference exampleThin Film Interference IIDiffraction from a slitOverlapping diffraction patternsDiffraction gratingsChap. 23-24: Refraction & Ray opticsRefractionTotal internal reflectionSlide 20Different object positionsEquationsSlide 23Chapter 26: Electric Charges & ForcesCharges conductors & insulatorsElectric force: magnitude & directionForces add by superpositionChapter 27: The Electric FieldElectric fieldPictorial representation of E: Electric Field LinesElectric field linesElectric dipoleQuick quiz: continuous charge dist.Force on charged particleDipole in an electric fieldElectric torque on dipolesDipole in non-uniform field1Physics 208 Exam 1 Review2Exam 1 Mon. Sep. 29, 5:30-7 pm, 2103 Ch (here)Covers 21.5-7, 22, 23.1-4, 23.7, 24.1-5, 26-27 + lecture, lab, discussion, HW8 1/2 x 11 handwritten note sheet (both sides) allowedChap 21.5-7, 22Waves, interference, and diffractionChap 23Reflection, refraction, and image formationChap 24Optical instrumentsChap 26Electric charges and forcesChap 27Electric fields3Alternate Exam TimeTuesday Sep. 30, 5:45 pm - 7:15 pmMonday Sep. 29, 6:00 pm - 7:30 pmYou must request one of these exam times by following the instructions at learn@uw. Check back to see if your request is approved. For students with scheduled class conflicts4Properties of wavesWavelength, frequency, propagation speed related asPhase relationIn-phase: crests line up180˚ Out-of-phase: crests line up with troughTime-delay leads to phase differencePath-length difference leads to phase difference€ λf = v5Ch 22, 21.5-7: Waves & interferencePath length difference and phasedifferent path length -> phase difference.Two slit interferenceAlternating max and min due to path-length differencePhase change on reflectionπ phase change when reflecting from medium with higher index of refractionInterference in thin filmsDifferent path lengths + reflection phase change6Phase difference & interferencePath length difference dPhase difference = d(2π/) radiansConstructive for 2πn phase differenceLShorter pathLonger pathLight beamFoil with two narrow slitsRecording plate7QuestionYou are listening to your favorite radio station, WOLX 94.9 FM (94.9x106 Hz) while jogging away from a reflecting wall, when the signal fades out. About how far must you jog to have the signal full strength again? (assume no phase change when the signal reflects from the wall)A. 3 mB. 1.6 mC. 0.8 mD. 0.5 mdxd-xpath length diff = (d+x)-(d-x)= 2x=3.16 mHint: wavelength = (3x108 m/s)/94.9x106 HzDestructive 2x=/2x=/4Constructive make 2x=x=/2x increases by /4 = 3.16m/4=0.79m8Two-slit interference9Two-slit interference: path lengthyL€ ≈d sinθ ≈ d y /L( )Path length difference € ≈2πd sinθλ≈2πdλy / L( )Phase differenceConstructive int:Destructive int.Phase diff = Path length diff = Phase diff = Path length diff = € mλ, m = 0,±1,±2K € 2πm, m = 0,±1,±2K € 2π(m +1/2), m = 0,±1,±2K € (m +1/2)λ, m = 0,±1,±2K10Reflection phase shiftPossible additional phase shift on reflection.Start in medium with n1, reflect from medium with n2n2>n1, 1/2 wavelength phase shiftn2<n1, no phase shiftDifference in phase shift between different paths is important.11Thin film interferenceair: n1=1n2>11/2 wavelength phase shiftfrom top surface reflectiontairair/nExtra path lengthExtra path length needed for constructive interference is No phase shift frombottom interface€ m +1/2( )λair/n( )€ ⇒ 2t = m + 1/2( )λair/n( )air: n1=1Reflecting from n2Reflecting from n112Thin-film interference exampleCoated glass in air, coating thickness = 275nmIncident white light 400-700nmGlass infinitely thickWhat color reflected light do you see?Both paths have 180˚ phase shiftsSo only path length difference is importantnfilm=1.2nglass=1.5nair=1Incident lighteyet=275nm€ 2t = mλair/nfilm€ m = 1 ⇒ λ = 660nm13Thin Film Interference IISame coated glass underwaterNow only one path has 180˚ phase shiftnfilm=1.2nair=1Incident lighteyenglass=1.5nwater=1.33€ 2t = m +1/ 2( )λair/ nfilm€ λair= 2tnfilm/ m + 1/2( )= 2 275nm( )1.2( )/ m + 1/2( )m=0 gives 1320 nm, too long. m=1 gives 440 nmColor changes underwater!14Diffraction from a slitEach point inside slit acts as a sourceNet result is series of minima and maximaSimilar to two-slit interference.Angular locations of minima (destructive interference)15Overlapping diffraction patternsTwo independent point sources will produce two diffraction patterns.If diffraction patterns overlap too much, resolution is lost.Image to right shows two sources clearly resolved.AngularseparationCircular aperture diffraction limited: € θmin=1.22λD16Diffraction gratingsDiffraction grating is pattern of multiple slits.Very narrow, very closely spaced.Same physics as two-slit interference € d sinθbright= mλ, m = 0,1,2K€ sinθbright= mλd17Chap. 23-24: Refraction & Ray opticsRefractionRay tracingCan locate image by following specific raysTypes of imagesReal image: project onto screenVirtual image: image with another lensLens equationRelates image distance, object distance, focal lengthMagnificationRatio of images size to object size18RefractionOccurs when light moves into medium with different index of refraction.Light direction bends according toi,1r2Angle of refractionn1n2€ n1sinθ1= n2sinθ2Special case:Total internal reflection19Total internal reflectionTotal internal reflection occurs A) at angles of incidence greater than that for which the angle of refraction = 90˚B) at angles of incidence less than that for which the angle of refraction = 90˚C) at angles of incidence equal to 90˚D) when the refractive indices of the two media are matchedD) none of the above201) Rays parallel to principal axis pass through focal point.2) Rays through center of lens are not refracted.3) Rays through F emerge parallel to principal axis.Lenses: focusing by refraction FFObjectImageP.A.Here image is real, inverted, enlarged21Different object positionsImage (real, inverted)Image (real,
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