Jquery dynamic dropdown event not firing

Question

Hi i am trying to create dropdownlists dynamically and populating the contents via an ajax call, this sort of works in the sense that the drop down is created and populated as required but its 'change' event does not fire. I am posting the code below, if anyone can spot something obvious, can you please let me know regards

$(document).ready(function () {

    $("#positions select").change(function (e) {
        alert("in");
        var id = $("#category_id").val();
        $.getJSON("/Category/GetSubCategories/" + id, function (data) {
            if (data.length > 0) {

                alert(data.length);
                var position = document.getElementById('positions');
                var tr = position.insertRow(7);
                var td1 = tr.insertCell(-1);
                var td = tr.insertCell(-1);
                var sel = document.createElement("select");
                sel.name = 'sel';
                sel.id = 'sel';
                sel.setAttribute('class', 'category');



                td.appendChild(sel);
                $.each(data, function (GetSubCatergories, category) {
                    $('#sel').append($("<option></option>").
           attr("value", category.category_id).
          text(category.name));

                });
            }



        });
    });
});