Question: i have added a splash screen to my application by adding Default.png.
the splash screen works fine in the simulator but not showing on real device

Answer: 
Sometimes this issue hapens, when .png file was renamed from .jpg file. 
So, for example, you had image.jpg, you've renamed in to image.png, and using this image.png. It'll be correctly displayed in simulator, and won't work on device
Select your Default.png in the groups and files window and make sure in the file listing above the editor window that the checkbox on the far right is checked. Without this the file will not be copied to the application bundle after compilation is finished.