Why should head be kept on northern side at the time of death?

The practice of placing the deadbody with head on the northern side...It brings forth the term 'prana'-life force..electric current generally flows from north to south..after death the prana is supposed to be present inside the body and not to come out of the body before the consignment to fire..but when the body is placed with head on the south side due to the flow of electric current,that may happen to leave the body which shouldnt happen..so the dead body is placed so..