Post model data containg file type using Ajax call in mvc4

I have a ViewModel containing some string and HttpPostedFileBase properties . When i am posting the model to the controller using below ajax call.

`$.ajax({`

`url: '@Url.Action("_AddFeedback", "Mcq")',`

`type: 'post',`

`data: $('form#frm-feedback').serialize(),`

`success: function (data)`

`{`

`alert("done"); },`

`error: function (data) {`

`alert("Error occured while saving Option's data."); } });`



I am getting value for string but null for HttpPostedFileBase type properties. How can we post HttpPostedFileBase file using ajax ??