The structure V + 一下 indicates the briefness of the action . When used in a request, it also makes the manner of speaking moderate and more polite. Somtimes the indication of briefness of the action is not very strong .
(1) 等一下 děng yī xià
Wait a minute.
(2) 停一下tíng yī xià Stop for a while.
3）你看一下 nǐ kàn yī xià Have a look.