Electromagnets. The electromagnetic relay
An electromagnet is a coil (solenoid) with an iron core inside. When current flows the field of the coil magnetises the core and the total field becomes much stronger; when the current is switched off, the field almost disappears. The strength of an electromagnet depends on the current, on the number of turns in the coil and on the presence of the core: a bigger current, more turns and a core give a larger force. Its poles are given by the right-hand rule; if the current direction is reversed, the poles swap. Electromagnets are used in cranes for lifting scrap iron, in electric bells, telegraphs and relays. A relay is a switch controlled by a small current: an electromagnet pulls an armature and closes the contact of another circuit carrying a large current; for example in the barrier (turnstile) mechanisms of a metro. The experiment is done only with a low-voltage source; never connect it to the mains.
Draw a diagram of an electromagnet and a relay in your notebook: core, coil, armature, contacts, two circuits (control and working). Do not make a real connection.