Win32_PhysicalMedia Problem

[C# Programming]

Hi all,

I am trying to execute this line of code but it not providing me the values

ManagementObjectSearcher pd = new ManagementObjectSearcher("SELECT Name, MediaType, MediaDescription from Win32_PhysicalMedia");
foreach (ManagementObject mp in pd.Get())
richTextBox3.Text += mp["Name"] + " " + mp["MediaType"] + " " + mp["MediaDescription"]; Can anybody please tell me what i am doing wrong or if i need to include something in this...
mainly i want to find media type...

Thanks in advance