The strength of an electromagnet depends on the current in the solenoid, the number of loops in the coil in the solenoid, and the type of ferromagnetic core. To increase the strength of an electromagnet, increase the current flowing through the solenoid. A greater current produces a stronger magnetic field. Increasing the number of turns, while keeping the same current, will also increase the field strength. Cores that are easily magnetized, such as “soft” iron, make stronger electromagnets.
What does the strength of an electromagnet depend on?
Electromagnetic Devices
Electromagnets can convert electrical energy into motion that can do work. 
Electromagnetic devices such as galvanometers, electric motors, and loudspeakers change electrical energy into mechanical energy. A galvanometer measures current in a wire through the deflection of a solenoid in an external magnetic field. An electric motor uses a rotating electromagnet to turn an axle. A loudspeaker uses a solenoid to convert electrical signals into sound waves you can hear.
Galvanometers
Figure 10 shows a galvanometer, a device that uses a solenoid to measure small amounts of current. A solenoid is attached to a spring and is free to rotate about an iron core. The solenoid is placed between the poles of two permanent magnets. When there is a current in the solenoid's coils, the resulting magnetic field attempts to align with the field of the permanent magnets. The greater the current, the more the solenoid rotates, as shown by the pointer on the scale. In an automobile fuel gauge, for example, a sensor in the gas tank reduces the current as the gas level decreases. This causes the needle to rotate towards the “empty” mark.
Figure 10 A galvanometer uses an electromagnet to move a pointer. One common application is in an automobile gas gauge. The pointer indicates the amount of current in the wire. The wire is connected to a sensor in the gas tank.
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