Submit <input type = "file" / "> with jQuery $ .post

I have a tag <div/>that contains a file upload tag <input id="file" type="file"/>. I want to publish the contents of a tag inputto a php page using $.ajax()or $.post(), but how can I capture the contents of a tag inputhaving its type as "file"? so can i send it using jQuery ajax functions?

Note. My code does not have a tag yet <form/>. I am not sure if it is required to download files. Also I saw some workarounds using <iframe>. I want to know if this can be done otherwise.

I do not want to use any plugins for this.