dH=dl/dt dB=dl/dx dE/dB=-dx/dt dD=dl/dx dH/dD=-dx/dt H - magnetic field strength; B - magnetic flux density; E - irradiance; D - electric displacement field. Please, have a look at these equations. Are they correct? I can't grasp the idea. Any explanations? I need some intuitive understanding of this formulas (if they are correct) and some knowledge about how they are derived... I will be grateful for every comment... Wish you everybody a nice day!!