CBSE Class 10 Answered

If you want to measure current you must break the circuit. If you are trying to measure current by connecting ammeter in parallel; there will be a seperate loop for current to travel through. Since most ammeter's measure current through a very small internal resistance; when connected in parallel nearly all the current will travel through the ammeter loop rather than the circuit. This is because the current will choose the path of the least resistance. Thus the limit of maximum current which can pass through ammeter is voilated. Hence the ammeter burns.
An ammeter will not always burn, because many of them have internal fuses that will blow if the power rating for the ammeter is exceeded.