Validate a checkbox before submit

checkbox.js

$(function(){
    $('#NationalPhotoMonth_submitButton').click(function() {
        if(!$('#NationalPhotoMonth_Field_48').is(':checked')){
            alert('Not Checked');
            return false;
        }
        if($('#NationalPhotoMonth_Field_48').is(':checked')){
            alert('Checked - GO');
            return true;
        }
      });
});