• who discovered the heating effect of electric current?
• who discovered electromagnetism?

James Prescott Joules discovered the heating effect of an electir curcuit.

The Danish physicist Hans Christian Ørsted (or Oersted written in the English alphabet) is normally said to be the first to connect electricity with magnetism when he noted in 1819 that a compass needle deflected toward a wire coil carrying electric current. 

This was later supported by experiments done by André-Marie Ampère in 1821, at the same time as Thomas Seebeck investigated heat-produced electromagnetism (the thermoelectric effect) in metals. 

The list of investigators is a long one, and includes Michael Faraday and Benjamin Franklin.