Transcript Slide 1
The electric field in an EM wave traveling northward oscillates up and down. In what plane does the magnetic field oscillate? 1) In the north - south plane. 2) In the up - down plane. 3) In the northeast - southwest plane. 4) In the northwest - southeast plane. 5) In the east - west plane. Recall: speed of mechanical waves along an elastic medium ~ T m Tension linear density E directly pushes charges (connecting distance charges), conveying the disturbance on one charge to others B induces back emfs to resist the changing E-fields v= E B while the mutually induced fields guaranteed EB Maxwell concluded disturbances in E, B field lines ripple out at constant speed 1 v= m 0e 0 In 1849 (Maxwell’s time) v= 1 m 0e 0 = 311,000,000 m/sec and Fizeau’s best measurement: c=315,000,000 m/sec Maxwell: “The velocity of the transverse undulations calculated from the electromagnetic measurements of MMs. Kohlrausch and Weber, agrees so exactly with the velocity of light calculated from the optical experiments of M. Fizeau, that we can scarcely avoid the inference that light consists in the transverse undulations of electric & magnetic phenomena.” The wavelength of microwaves generated by a microwave oven is about 3 cm. At what frequency do these waves cause the water molecules in your breakfast burrito to vibrate ? 1) 1 GHz 2) 10 GHz 1 GHz = 109 Hz 3) 100 GHz The magnetrons of microwave ovens are tuned to 2.54 GHz (the natural vibrational energy that sets water molecules spinning/flipping and heating up any surrounding food). 2.54 109 Hz 0.125 meter = 12.5 cm Infrared Photography Infrared photography is used to check heat insulation of houses in winter. If you look at an infrared picture of a house which areas would need better insulation? 1) the bright areas 2) the dark areas 3) need more information Oxygen O8 1s 2s 2p Iron 3s 26 Fe 3p 4s 3d 4p 5s 4d Energy Levels for Hydrogen Atomic Spectra Blackbody spectrum is continuous: But spectrum of a heated rarefied gas shows lines: Emission spectrum And when white light shines through a rarefied gas, dark lines appear in the continuous spectrum: Absorption spectrum Explaining these phenomena requires and understanding of the atom Some answers to previous slides: 5) In the east - west plane. In an electromagnetic wave, the E and B fields are perpendicular to each other and to the direction the wave propagates. 2) 10 GHz f = v / = 3 108 m/s / 0.03 m = 1010 Hz = 10 GHz 1) the bright areas