solenoid

A relay is a device that allows a small amount of electrical current to control a large amount of current. A car starter motor uses a relay to solve the problem that a car has in needing a large amount of current to start the engine. A starter relay is installed in series between the battery and the starter. Some cars use a starter solenoid (as shown here) to accomplish the same purpose of allowing a small amount of current from the ignition switch to control a high current flow from the battery to the starter.

The irregular movement of dust particles becomes visible in the air when the particles are caught in a ray of sunlight. The tiny dust particles move randomly as they are buffeted by gas molecules in the atmosphere, which are too small to be seen with the naked eye.

Coil of wire, usually cylindrical, in which a magnetic field is created by passing an electric current through it (see electromagnet). This field can be used to temporarily magnetize, and so move, an iron rod placed on its axis. Mechanical valves attached to the rod can be operated by switching the current on or off, so converting electrical energy into mechanical energy. Solenoids are used to relay energy from the battery of a car to the starter motor by means of the ignition switch.

The solenoid has a magnetic field, one end being the north pole and the other end the south pole. A solenoid behaves like any other electromagnet; by changing the direction of the current the position of the north and south poles can be switched. If a larger current is passed through the coil it becomes a stronger magnet.