Sensitivity Factors of a Galvanometer

The galvanometer is a device used to measure the electric current’s presence and determine small current’s magnitude. This instrument detects the small electric current by showing deflection in the needle present inside the galvanometer. It is used in bridges and potentiometers where it indicates zero electric currents.

When does the galvanometer show a deflection? Besides the flow of current, what factors does the galvanometer deflection depend on? The answer to this is that the deflection is calculated based on current in the coil, magnetic field, and area and on many other factors, which we are discussing further here.  

How to Construct a Galvanometer

The galvanometer consists of an iron cylinder encapsulated, a coil covered with a frame, a magnet, rod, and pivot, and a magnetic needle that works as an indicator. The needle indicates the presence of the current, which determines the sensitivity of galvanometers. We’ll see this in the topic, the sensitivity of the galvanometer. 

A light rectangular frame on which a coil of thin copper wire is wound is pivoted between two almost frictionless pivots and placed between the cylindrical poles of a permanent magnet so that it can freely rotate in the region between the poles. The poles are suitably shaped, and a small soft iron cylindrical core is placed at the axis of the coil to obtain a uniform magnetic field. When the current is passed through the coil, a torque acts on it and is deflected. This deflection causes the restoring torque in the spiral strings attached at the two ends of the coil to attain a steady deflection. The pointer attached to the coil moves on a scale and indicates the current. 

What is The Working of Galvanometers?

The galvanometer works on the principle of converting electrical energy to mechanical energy. Also, the galvanometer provides the direction and magnitude of the current produced. The deflection produced in galvanometers determines the sensitivity of galvanometers. Did you know what the sensitivity of galvanometers is? It is the deflection ratio produced by the galvanometer when current flows through it. 

When current starts flowing in the coil, it moves up from one side, and from the other side, it moves downwards in the coil. The scale of galvanometers can be appropriately calibrated to measure the current. To measure peak currents of the order of 10-11 A, galvanometers with coils suspended by an elastic fibre between appropriately designed magnetic poles are used. 

The torque developed in the coil due to current passing through it is explained by τ = NiABsinθ

Where N = Number of turns of the coil

               I = Current through the coil

               A = Area of coil

               B = Magnetic intensity

               = Angle between area vector of coil and direction of magnetic intensity 

As the magnetic field is radial, is 90° in any position of the coil, and sin 90° is 1. 

The restoring torque produced in the springs is directly proportional to the deflection of the coil. ∴ τ = k∅

Where K = effective torsional constant

For steady deflection ∅, NiAB = k∅

∴ i = k /NAB∅

From the derived equation above, we can conclude that ∅ is directly proportional to i.

What is The Sensitivity of The Galvanometer?

A galvanometer is said to be sensitive if there is a distinct deflection when a decent amount of current is passed through it. The sensitivity can be described as either due to current, termed as current sensitivity, or due to voltage, termed as voltage sensitivity. 

Current Sensitivity 

A galvanometer’s current sensitivity is the deflection generated when unit current passes through it. When a galvanometer produces a considerable deflection for a tiny current, it is said to be sensitive.

Current sensitivity θ/I = nBA/C

Where c is Twisting couple per unit twist

A galvanometer’s current sensitivity can be enhanced by

• Increase in the greater number of turns
• A boost in magnetic induction
• Enlarging the coil’s surface area
• Lowering the suspension wire’s coupling per unit of twist

Voltage Sensitivity 

It measures an appliance’s responsiveness to a voltage transform applied across it. An ammeter is also a variety of galvanometers. It’s an instrument that determines electric currents, due to which voltage sensitivity of any galvanometer can be constituted as the per unit of voltage deflection over the galvanometer.

Voltage sensitivity = θ/V = θ/IG = nBA/CG

A galvanometer’s voltage sensitivity can be enhanced by:

• The smaller the spring constant and the greater the voltage compassion, the softer the spring and the lower the spring constant.
• The resistance will be lower, and the voltage sensitivity will be higher as the wire becomes thicker.
• The sensitivity of voltage will increase as the number of turns increases.
• The sensitivity of voltage will increase as the magnetic field becomes stronger.
• The greater the area, the greater the sensitivity.

What are The Sensitivity Factors of Galvanometers?

The current produced in galvanometers depends on various factors, including the coil’s area, magnetic field, number of turns, and torque. 

When the number of turns increases, the current produced in the coil also increases, as the current is directly proportional to the number of turns that the coil has. Similarly, the current flowing in the torque depends on the other three terms, as all these quantities determine the torque when the current flows through it. When the magnitude of the magnetic field increases, it also increases the current flowing through the coil. 

Conclusion

To conclude, the galvanometer is the electromagnetic instrument used to determine the presence of electric current. The galvanometer works on the principle of converting mechanical energy to electrical energy. The galvanometer also provides the direction and magnitude of the current produced. It consists of an iron cylinder, a magnetic needle that shows deflection, a magnetic rod, a pivot, and a coil that is encapsulated in the frame. A torque is applied to the coil when current passes through it. The coil rotates due to the magnetic torque. The spring acts as a counter torque, balancing the magnetic torque and resulting in a constant angular deflection.