Responsive media query not working for browser re size on pc

[Riya]

I am making a responsive design for my website. I have made two separate css files for this:\[code\]<link rel="stylesheet" type="text/css" media = "screen and (min-device-width: 500px) and (max-device-width: 1500px)" href="http://stackoverflow.com/questions/13779158/style.css" /><link rel="stylesheet" type="text/css" media="screen and (max-device-width: 500px)" href="http://stackoverflow.com/questions/13779158/mobile.css" />\[/code\]Its working fine when seen through any phone. But when I resize my browser on my pc the stylesheet does not change.I want both things to happen. Stylesheets should change in both cases - if the device width is changed or if browser window is resized.