How to stop timer in javascript

I'd want to end a timer by clicking a button, but I can't figure out how.

I tried using clearInterval() to halt a timer, but I'm not sure whether it was called correctly.

This is my current code.

<html>
<head>
    <title>Bootstrap</title>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="stylesheet" type="text/css" href="setest_style.css">
    <link href="https://cdn.bootcss.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

    <script type="text/javascript">
      var sec = 0;
      
      function pad(val) {
        return val > 9 ? val : "0" + val;
      };
      
      setInterval( function(){
        $("#seconds").html(pad(++sec%60));
        $("#minutes").html(pad(parseInt(sec/60,10)));
      }, 1000);
      
      function myStopFunction() {
        clearInterval(sec);
      }
    </script>
</head>
<body>
    <div class="quiz-time">
        <div class="timer">
            <span id="minutes">00</span>:<span id="seconds">00</span>
        </div>
        <button href="#" id="show-explanation" class="button1" onclick="myStopFunction()">Stop</button>
    </div>
</body>

</html>