Bimetals - These are metals created by joining two separate metals. Or one can say with layers or different metals. Trimetals - Trimetals also referred to as Tetrametal are metals which consists of three or four layers of different metals.
Copper is a very good electric conductor, it has been used in electric wiring since 1820s. It was with Telephone's invention that demand for copper wire sky rocketed. Largely used in Power Generation, Telecommunications and countless electrical equipment’s.
These are Clocks like devices with special electronic just for them. It is much more accurate than mechanical timers. With digital.
Relays are a kind of switches and its work is to open and close circuits electronically or electromechanically. The same it is in PCBs.