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>