Beginner Problem How do I connect to php file

Beginner Problem How do I connect to php file

I have type many Jquery examples non give me a return from the php file.  Do I need to reset permissions?

The most basic example is:
HTML file:


<html>
<head>

<script type="text/javascript"> 

$(document).ready(function() {
$('feedback').load(check.php).show();

        });

</script>


</head>
<body>

<form name="form">
Username: <input type="text" id="username_input" name="username">
</form>
<div id="feedback">This is where return value will be placed </div>




</body>
</html>

//////////

PHP file:

<?php

echo "Some Data from php page";





?>