Frequency & Wavelenght of EM wave!! Hi..on some other thread i found this link showing animation of propagation EM wave: http://www.molphys.leidenuniv.nl/monos/smo/index.html?basics/light_anim.htm [Broken] it has cleared my one doubt, because i used to think that EM wave is like an invisible line in air which moves up and down like sinusoidal manner. But it actually a variation in electromagnetic field. But then my question is: the frequency of the EM wave is the frequency of electric & magnetic field variation( as AC voltage)? and how wavelength is measured since there is no(physical) peaks to measure distance between?