i wasnt sure where to put this so feel free to move it, mods, if its in the wrong place. just reviewing for my optics final and im trying to work out a question. but i think the formula i got for it isnt right. QUESTION: The linewidth of a green light (lambda= 500nm) is DELTA-lambda=2.5 X 10^(-3) nm, what is the frequency bandwidth DELTA-nu? a) 3X10^8 Hz b) 3X10^9 Hz c) 3X10^6 Hz d) 3X10^-8 Hz e) none o the above SOLUTION: i have the forumla....DELTA-nu= (-c / lambda)*DELTA-lambda....my prof gave us this forumula to use on the last day of class when we were going over these problems. but when i use it i dont get one of the answers listed. i know theres an option E, but he virtually never uses that. and also my answer is 1500 which is off by a factor of 2 X 10^x....i found that odd. and lastly when you compute the units of the above mentioned forumla you end up with m/s...shouldnt the units be in 1/s? i must have this formula wrong.