Single terminal of battery alone connected to earth.
I took a 12 Volt battery and connected its positive terminal to one end of LED bulb with enough series protection resistor. Then i connected the other end of the LED bulb to earth (soil with moisture outside my house). I did not connect negative terminal of the battery to anything. I expected the bulb to glow. But it did not glow until i connect the negative terminal also to ground. While there is potential difference between earth and battery why dont current flow through bulb when i did not connect negative terminal to earth.
I have attached the photo of the battery that i used. I am sure that LED's were working properly and battery had enough capacity to provide current.