File not find during link

I'm working in a Linux system ( Ubuntu 12.04 ), using ifort linking the main program main.f90 and library lib.a. If I use command

ifort main.f90 /home/tom/lib/lib.a

then everything is fine. But if I use

ifort -L/home/tom/lib main.f90 lib.a

then ifort gives an error

ifort: error #10236: File not found:  'lib.a'

Why the -L specification doesn't work? When I want to use the environment variable LIBRARY_PATH ? It still gives me that error, why that happen? Must I specify the full path every time I link the library?