selected value from dropdownlist in mvc3

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MVC3

i bind a dropdownlist by a viewdata which have display member and value member in mvc3.
i write code to get selected value using jquery. but don't get the any value from dropdown list

my code is
var value = $("#s1 option:selected").val(); not get any value

var value = $("#s1 option:selected").text(); get selected text

but i want selected value from dropdownlist