How to use ng-model in select button

<!DOCTYPE html>
<html>
<script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.4.8/angular.min.js"></script>
<body ng-app="">

<form>
  Select a techonoly:
  <select ng-model="my">
    <option value="">
    <option value="py">Python
    <option value=".net">.Net
    <option value="aj">AngularJs
  </select>
</form>

<div ng-switch="my">
  <div ng-switch-when="py">
     <h1>Python</h1>
     <p>General purpose programming language</p>
  </div>
  <div ng-switch-when=".net">
     <h1>.net</h1>
     <p>Microsoft framework for c#</p>
  </div>
  <div ng-switch-when="aj">
     <h1>AngularJs</h1>
     <p>Javascript framework from google</p>
  </div>
</div>

</body>
</html>