Physics
Why Do Electrical Sparks Appear When Unplugging Appliances?
Quick fact
The spark you see when unplugging an appliance is a miniature electrical arc: the air in the gap becomes briefly conductive because the voltage causes it to ionize, and a current continues to flow until the gap is too wide to support it.
Why this is interesting
You yank the charger out of the wall and see a tiny blue flash. Why does electricity arc out of a socket that should be closed when nothing is connected?