Edit in JSFiddle

$(function () {
    $('.accordionPanel').hide();
    $('input').click(function () {
        var num = $('input').index(this);
        //var object = $('.accordionPanel').get(num);
        var object = $('.accordionPanel').eq(num);
        $('.accordionPanel').not(object).hide();
        object.show();
    });
});

<input type="radio" name="accordion" class="ac" value="0" checked/>
<label for="ac01">radio1</label>
<input type="radio" name="accordion" class="ac" value="1" />
<label for="ac02">radio2</label>
<input type="radio" name="accordion" class="ac" value="2" />
<label for="ac03">radio3</label>
<div class="accordionPanel"></div>
<div class="accordionPanel">パネル02</div>
<div class="accordionPanel"></div>