2. What is the wavelength of an EM wave ? Wavelength is related to wave’s frequency f.  f = c (speed of light) The higher the frequency of a wave, the shorter its wavelength.

3.  f = c c = 3x10 8 m/s Examples: Commercial AM Radio: f: 550 khz to 1600 khz : 545 m to 187 m Commercial FM Radio: f: 88 Mhzto108 Mhz :3.4 mto806 Mhz Microwave Oven: f = 2.45 x 109 Hz = 12 cm

4. Various Applications of the EM Spectrum We can use EM waves to probe the structure of objects. Their wavelength must be comparable to the size of the object.

5. Applications of Radio Waves Radio, TV, Cellular Phones Left: Radio Telescopes (dish size ~ 64 m) Above: VLA – Very Large Array telescope 27 antennas, 36 km across

6. Applications of Microwaves Microwave ovens Communications ‘Doppler Radar’ Remote Sensing: (Left) Ice breaking off Alaska shore (Right) Amazon River Fluctuating Microwave Background around Earth: Remnants of the ‘Big Bang’

7. Today: Focus on Visible Spectrum

8. Some Observations about Sunlight Looks like it’s colored ‘white’ Sky appears blue and during sunset/sunrise: redder Reflects from many surfaces Separates into various colors after passing thru materials After raining, we sometimes see Rainbows

9. Rayleigh Scattering