Having recently been in a group perfoming an ESR experiment I'm still not sure of how it works. OK ESR relies on free radicals, unpaired electrons. Electrons split into alignment with field in one of 2 states, spin-up & spin-down & the magnitude is equivalent to h bar*B*gamma (gyromagnetic ratio) When electromagnetic wave of angular frequency, ω, is applied we can find the g-factor. So the thing which I'm detecting through the detectors at the magic T & cavity is the spin of the electrons is it? If the spin is from unpaired electrons then why am I not detecting th same things for everything as electrons are all the same? Is it the case that the material being considered changes the display on the oscilloscope due to different energy absorbtion. Have I just answered my own question? Could you briefly nudge in the right direction as to what I'm trying to find when using microwaves to detect electron spin resonance, i.e. what results or physical effect would you be expecting me to put in the report. (also measure gyromagnetic ratio & ESR linewidth) Thank you.