When we restore file\file group(backup1) backup on a database is it necessary to restore all log backups that were taken after backup1 to get database in consistent state?? and also what will be the impact of log restore process on database state and those files?
Yes - if you want to completely bring your database online (with all file groups) or you want to do a point-in-time restore of your database.
No - if you want to do a piece meal restore for specific file group.
I have explained in detail by giving an example at Backing up file groups with restore to earlier backup.