Electromagnetic Waves ------------------------------------------- Joseph F. Alward, PhD     Department of  Physics   University of the Pacific

 

Click here to see animation of the creation of electromagnetic wave from an oscillating charge.

  The Electromagnetic Spectrum                                               

   Wavelengths                                                                                            

   Wavelengths of Visible Light                                                   

                                                                                                     

Green light:  l = 500 nm                                 f = c/l =3 x 108 / 500 x 10-9 = 6 x 1014 Hz

  Measuring the Speed of Light                                        

Find minimum rotational speed for observer to view light. -------------------------------------------------- Mirror rotates 536 times per second. Eight faces:  4290 faces per second One face is replaced by the next every 1/4290 second. Light travels round trip:  70 km 70 x 103 x 4290 = 3 x 108 m/s

  Supernova and the Speed of Light                                                      

One light-year is the distance light travels in one year. c = 3 x 108 m/s -------------------------------------------- Number of seconds in one year: (365.25)(24)(3600) -------------------------------------------- 1 light year (LY) = 9.47 x 1015 m

    Doppler Radar                                                                                                  

u = relative speed           Moving Toward:                   Moving Away:                                              f = f '(1 + u / c)                        f = f ' (1 - u / c)

    Doppler Example                                                                                          

f   = frequency broadcast by police car              f ' = frequency received and reflected by speeding car              f " = frequency received by police car