PictuerBox1.ImageLocation property

Question

I want to use property ( PictuerBox1.ImageLocation) but I found that this property returns null. I don't understand how???
 
PictureBox pb = new PictureBox();
Image loadedImage = Image.FromFile("C:\\Documents and Settings\\All Users\\Documents\\My Pictures\\Sample Pictures\\Winter.jpg");
pb.Height = 50;
pb.Width = 50;
pb.Image = loadedImage;
string s = pb.ImageLocation;