A galvanometer is a device used in the electric field to detect the slightest amount of current in an electric field. It has a magnetic needle or a coil in its setup. The movement of this magnetic needle or coil shows current intensity. A galvanometer is a sensitive device. Using a galvanometer, current can be measured in the form of a millimetre, milliamperes, or microampere. Let’s see the working principle, application, structure, and functions of galvanometers in detail. 

The working principle behind the galvanometer

The working principle behind the galvanometer is as follows: 

• When a current-carrying coil is suspended freely in a magnetic field, a torque acts upon the coil. Due to the torque, the coil rotates. 
• The deflection of the coil is directly proportional to the current flowing through the coil. 

The torque acting in the coils is given by 

τ = nIAB

where, 

n = the number of turns of coils

I = current

A = area of the coil

B = perpendicular distance between the forces. 

The deflection in the coil given by θ is given by 

θ= (nAB / k)I 

where k is the torsional constant of the string. 

Structure of galvanometer

• It is made of a rectangular coil having many turns
• The coil is made of thinly insulated or fine copper wire wound on a metallic frame, and it is free to rotate about a fixed axis.
• The coil is suspended in a uniform radial magnetic field by a phosphor-bronze strip connected to a movable torsion head. 
• Phosphor bronze strip has good conductivity and a low value of the torsional constant. 
• An iron core is kept symmetrically inside the coil to make the field radial and improve the strength of the magnetic field. This iron core is soft and has a cylindrical structure. 
• The upper end of the coil is connected to binding screws, and the lower end is attached to a phosphor-bronze spring. This spring has many small turns. 

Functions of galvanometer

From the above introduction, we know that the function of a galvanometer is to detect the small amount of current flowing through a circuit. Let’s look at the actual way of functioning of the galvanometer now. 

A galvanometer is a coil with many turns placed in a very strong magnetic field. The more the number of turns, the more current flows and produces more torque. Thus, torque will be more in a strong magnetic field. 

A coil starts rotating when the small current, which needs to be detected, is sent through it. The torque acting on the coil due to the current makes it rotate. The number of deflections produced by the coil is measured using a pointer and a scale. 

Thus, more current leads to more torque, which in turn leads to more deflection, ultimately increasing the scale reading. 

Applications of a galvanometer

Galvanometers have a wide range of applications. A few of them are as follows:

1. They were used as display components to capture the sensor outputs of other types of analogue measuring devices like light metres and light VU metres. D’Arsonval galvanometers or Weston type of galvanometers are widely used today.
2. The use of galvanometer-driven pens in strip chart recorders can give an all-out frequency response of one hundred Hz. Also, they help in identifying the deflections happening in centimetres.  
3. A mechanism like that of the moving coil of a galvanometer, called ‘voice coils’ by disk manufacturers, is used in hard disk drives and CD/DVD players to dominate the pinnacle positioning servos. 
4. A galvanometer helps in determining the TV voltage between two points easily.
5. A mirror galvanometer, which has a high power galvanometer mechanism, is used in high-power lasers for material processing. They are usually used with closed-loop servo control systems.

Conclusion

Thus, it can be concluded that the function of a galvanometer is to detect the small amount of current flowing through a circuit. The working principle behind the galvanometer is, “a current-carrying coil, when placed in a magnetic field, experiences a torque”. More current leads to more torque, which leads to more deflection, ultimately increasing the reading on the scale of a galvanometer. Nowadays, D’Arsonval galvanometers or Weston type of galvanometers are widely used. Phosphor bronze strip is used in galvanometers because it has good conductivity and a low value of the torsional constant.