A wire of length '\( L \)' and radius '\( r \)' is clamped rigidly at one end. When the other end of the wire is pulled by a force \( f \), its length increases by '\( l \)'. Another wire of same material of length '\( 2L \)' and radius '\( 2r \)' is pulled by a force '\( 2f \)'. Then the increase in its length will be:
