Light, Wave - Electricity and Optics - Lecture Slides, Slides of Electrical Engineering

Download Light, Wave - Electricity and Optics - Lecture Slides and more Slides Electrical Engineering in PDF only on Docsity! 1 LECTURE 22 4/2/12 2 White Light: A Mixture of Colors (DEMO) 4/2/12 3 White Light: A Mixture of Colors (DEMO) 1. Add together magenta, cyan, and yellow. Play with intensities of each to get white light. 2. Try to make white light out of blue, red, green light. 3. Take look at shadows that result from putting an object in the light path. 4/2/12 4 Spectral Lines Energy states of an atom are discrete and so are the energy transitions that cause the emission of a photon (DEMO) 2 4/2/12 5 Emission spectra are produced by thin gases (few collisions). The emission lines correspond to photons emitted when excited atomic states in the gas make transitions back to lower-lying levels. Continuum spectrum: Solids, liquids, or dense gases emit light at all wavelengths when heated. Absorption spectrum occurs when light passes through a cold, dilute gas. Atoms in the gas absorb at characteristic frequencies. Re-emitted light is unlikely to be emitted in the same direction dark lines in the spectrum. 4/2/12 6 Dependence of Intensity on Distance power Pav Consider spheres at different radius from the source emitting the EM radiation 4/2/12 7 Intensity I, power Pav, pressure Pr, energy density uav, etc. of EM waves. 4/2/12 8 Transfer of Momentum A t Up I c c IAF c ΔΔ = = = 22 2 A t Up I c c IAF c ΔΔ = = = Pressure P = F/A, so Pr = I c Pr = 2I c )(momentumpp =Δ )(2 momentumpp =Δ Total Absorption Total Reflection time momentum t pF = Δ Δ= U IA tΔ = Δ