Using a jQuery Selector With a Variable

Is there any way to make something like the following code?

var input = ("$(\"#div .input[id='" + id + "']\")");
input.fadeIn();

Or maybe I could use something like the following?

var input = ("\"#div .input[id='" + id + "']\"");
$(input).fadeIn();

PS: Take my apologies as this question was cloned but the answers that I found were too ambiguous.