Where is the file when I upload it?

I’m building an app, using RoR and activeAdmin, where the user can
upload a
file. I have asemantic_for_form which contains this:<%= f.input
:uploaded_data, :as => :file %> and a method which is in charge to read
the
file uploaded by the user. My question is: where this file is upload?
where
the program stores it?
Thanks!