jquery - I am getting response from php but not printing in text box -

i have 2 files, 1 html , jquery , other php.
getting response php page, not able display in html text box.

here code:

<script type="text/javascript"> function fill_amt() {   var sname=$("#sname").val();   $.post("try_insert.php",{sname:sname,cmd2:"fill_amt"},function(data){   $("#tot_amt").html(data);   }); } </script> 

here html code:

<input type="text" id="tot_amt" name="tot_amt"> 

here php code

$sql = mysql_query("select total_fee admission first_name='".$sname."'")or die(mysql_query()); $val=mysql_fetch_row($sql); $tot=$val; echo json_encode($tot); 

use:

$("#tot_amt").val(data); instead of $("#tot_amt").html(data);

also format json data correctly.