When a piece of iron is placed inside a solenoid which is carrying current, the iron becomes strongly magnetized. The strength of the magnet will depend on: (a) the number of turns in the coil; the larger the number the stronger the magnetism; (b) the strength of the current-the larger the current the stronger the field; and (c) the nature of core material. When the current is switched off, the iron ceases to be a magnet. This arrangement is called an electromagnet. It is an essential part of electric generators, motors, telegraph instruments, loudspeakers, earphones and telephone receivers.