What cause extreme heat when electricity connect to it?
The overarching principle is that conservation of energy applies in a closed system. See https://en.wikipedia.org/wiki/Conservation_of_energy

A very common example of this the combustion of fuel in a spark-ignition engine. See https://en.wikipedia.org/wiki/Spark-ignition_engine, https://en.wikipedia.org/wiki/Otto_cycle  

An extreme example would be triggering a nuclear explosive.  

In these these examples the potential (stored) energy in the device is liberated as heat, mechanical action, etc; after the reaction has been initiated by a bit of heat provided by electrical system.