After asking a professor a question through e-mail and receiving an answer, is it polite that a student send a short e-mail simply saying "Thanks" as an acknowledgment that the answer was received and appreciated? I'm thinking of sending this but am not sure if it might be considered annoying or unnecessary (as I'm not sure how busy the professor is, or how many emails he/she has to sort through every day.)
Is there some widely agreed-upon etiquette for this?