What is the difference between فعل and عمل?

Allah (SWT) in some places in the Quran uses فعل and in other places uses عمل. - 2:68 - فافعلوا ما تومرون - 41:40 - اعملوا ما شئتم Is there a difference between them linguistically or semantically that can give us more insight into the commands of Allah? I once read somewhere in a tafseer, that فعل is like hearing and seeing (passive), عمل is like listening and watching (active). I can't find it though.