i hope you are from tamilnadu, i dont about know about electrical engineering because iam from management, regarding history, follow ncert old editions +1&+2, books new editions are not tailored for civil service, so buy old ones it will be available in old book shops if you are in chennai you can easily get the old books, i can't assure even you finish entire book of ncert,even state board text for history is also having some of the details that ncert didn't have and also spectrum gnereral studies manual is also useful,if you combine and study all these books surely you can get through in history and note making is important, all the best.