jquery event handler inside updatepanel not working

jquery event handler inside updatepanel not working

I have drop downlist  inside upadate panel. My jquery change function not working. could you explain why

$(document).ready(

function () {

$(

"#ddlRateStructure" ).change( function () {

alert(

"It worked!" );

});

})

...
< asp : UpdatePanel ID ="UpdatePanel1" runat ="server">
< ContentTemplate >
....

<

div class ="td">

< asp : DropDownList runat ="server" ID ="ddlRateStructure" ClientIDMode ="Static" >

</ asp : DropDownList >

</ div >

....
</ ContentTemplate >
</ asp : UpdatePanel >