The correct answer is the magnetic effect of current. Hans Christian Oersted, a Danish physicist and chemist, was the first to discover the connection between electricity and magnetism in 1820. This pivotal experiment demonstrated that an electric current in a wire could produce a magnetic field around it, which was initially observed when a magnetic compass needle was deflected by a nearby electric current. This discovery led to the development of electromagnetism and had a significant impact on technology and physics as it laid the foundation for the study of electromagnetic fields.
Hans Christian Oersted was the first to experimentally show that an electric current produces a magnetic field. In his experiment, he observed that a compass needle got deflected when placed near a current-carrying wire. This discovery established the link between electricity and magnetism.
Hence, his demonstration is related to: magnetic effect of current