Let There Be LightWhere are we?Slide 3Slide 4Glare tends to beSlide 6Slide 7Measuring the speed of light without electronics … the olden days24.3 The Speed of Lightmore on polarizationFrom capacitor and coil we foundIntensityE and B are cousins!more on PolarizationSlide 15MALUS’ LAW24.6 PolarizationSlide 18Slide 19the experiment - mirrorsreflectionSlide 22Slide 23Get to work on mirrorsLet There Be LightLet There Be Light13.313.3Where are we?•Exam #3 on Monday Morning–Watch for another of those Webby Things•Today, we continue our study of optics and continue working with the optics kit.•Next week … optics marathon.Start readingchapter 24after the testWhich one of the following statements concerning electromagnetic waves is false?A) Electromagnetic waves are longitudinal waves.B) Electromagnetic waves transfer energy through space.C) The existence of electromagnetic waves was predicted by Maxwell.D) Electromagnetic waves can propagate through a material substance.E) Electromagnetic waves do not require a physical medium for propagation.The electric field E of an electromagnetic wave traveling the positive x direction is illustrated in the figure. This is the wave of the radiation field of an antenna. What are the direction and the phase relative to the electric field of the magnetic field at a point where the electric field is in the negative y direction?Note: The wave is shown in a region of space that is a large distance from its source.A) +y direction, in phaseB) –z direction, 90° out of phaseC) +z direction, 90° out of phaseD)–z direction, in phaseE)+z direction, in phase Think about the diagram we used yesterday and howthe charge moves to produce the wave in the first place!Glare tends to beA. un-polarized lightB. light polarized verticallyC. light polarized horizontallyD. the polarization depends on the conductivity of the material causing the glareWhich one of the following colors of visible light has the highest frequency?A) yellowB) redC) greenD) blueE) violetLike all waves, electromagnetic waves have a wavelength and frequency, related by:fc The speed of lightin a vacuumsm 458792299c sm1000.3AmT104mNC1085.811872212oocMaxwell’s prediction of the speed of lightThe total energy density carried by an electromagnetic wave222121Volumeenergy TotalBEuooMust contain moving energy1 Total energyP Energy uctAS cuA time Area t A tA= = = = =Maxwell’s Equations show that the energy density of the magnetic field and the electric field in an electromagnetic wave are the same.Consequently2 2002 2000 01 1 (Peak Values)2 21since1 getE=cBE E2 2rms rmsu E Bsou E BcweE Eememe m= += === =In polarized light, the electric fieldfluctuates along a single direction.Polarized light may be produced from unpolarized light withthe aid of polarizing material.IMPORTANT STUFF HERE2cosoSS intensity beforeanalyzerintensity afteranalyzer2 22 222sin cos 1sin cos2 cos 11cos2q qq qqq+ ====Example 7 Using Polarizers and AnalyzersWhat value of θ should be used so the average intensity of the polarizedlight reaching the photocell is one-tenth the average intensity of theunpolarized light?S0S0/2 221101cosooSS 251cos51cos 4.63Conceptual ClickerSuppose that a third piece of polarizing material is inserted between the polarizer and analyzer. Does light now reach thephotocell?A YesB NoC More info required.Complete the last one first.Prepare to Discuss These Problems After The Experiment:1.A friend is standing 2 m in front of a plane mirror. You are standing 3 m directly behind your friend.2.How far is your image behind the mirror?3.What is the distance between you and the image of your friend?4.Suppose that you are walking perpendicularly with a velocity of +0.90 m/s toward a stationary plane mirror. What is the velocity of your image relative to you? The direction in which you walk is positive direction.I Feel
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