2 Lesson 1 Outline the nature of electromagnetic (EM) waves. Describe the different regions of the electromagnetic spectrum.Describe what is meant by the dispersion of EM waves.Describe the dispersion of EM waves in terms of the dependence of refractive index on wavelength.
6 Source of electromagnetic waves? You have 15 minutes to take notes from pages 600 and 601 about how different EM waves are produced.
7 Sources of EM radiation TypeSourceRadioVibrating electrons e.g. AC currentMicrowavesExcited semiconductors or vibrating electronsInfra-redElectrons transitions between energy levelsVisibleUltravioletX RayEmitted when decelerate rapidly electrons e.g. when they hit a metal targetGammaEmitted by nuclei after a nuclear reactionTypeSourceRadioMicrowavesInfra-redVisibleUltravioletX RayGamma
9 A reminder - Snell’s law speed in substance 1 sinθ1speed in substance 2 sinθ2=
10 A reminder - Snell’s law In the case of light only, we usually define a quantity called the index of refraction for a given medium asn = ccmwhere c is the speed oflight in a vacuum and cmis the speed of light in themediumcvacuumcm
11 DispersionThis occurs because the index of refraction of the glass changes with wavelength. The index of refraction is slightly smaller for red light than it is for blue light, so the red light gets bent less.