Moving Coil Galvanometer: Definition, Constructions, Working Principle, Application & Class 12 Notes

A moving coil galvanometer is an electrical device used for detecting and measuring small electric currents. It works on the principle of the Lorentz force law. When a current-carrying coil is placed in the magnetic field, it experiences torque, which causes the coil to rotate and show deflection on a scale.

Read More: NCERT Solutions

A moving coil galvanometer is an instrument which is used to detect and measure small electric currents. It works on the principle of the Lorentz force law, which states that a current-carrying coil experiences a torque when placed in a uniform magnetic field.

Diagram of a moving-coil galvanometer:

 

 Main Parts of the Moving Coil Galvanometer

A moving coil galvanometer is an instrument used to detect and measure small electric currents. It works on the principle of the Lorentz force law. This law state that a current-carrying coil will experience a torque when it is placed in a uniform magnetic field.

Main Parts of the Moving Coil Galvanometer

Rectangular Coil

• The coil is made up of insulated copper wire (thin wire).
• The wire is mounted on a lightweight aluminium or brass frame.
• The coil rotates between the magnetic poles.

Magnet

• A permanent horseshoe magnet is used in a galvanometer.
• Provides a radial magnetic field for uniform torque on the coil.
• To make the field radial and strong soft iron cylinder is placed between the poles.

Soft Iron Core

• It is cylindrical and placed between the magnet poles.
• Soft iron core concentrates and radializes the magnetic field.

Suspension System

• The coil is suspended by a fine phosphor bronze wire, which is both a support and a conductor.
• To provide restoring torque, a spring or lower suspension is also attached.

Pointer and Scale

• A light pointer is attached to the coil.
• Moves over a scale calibrated in divisions
• The pointer and scale show deflection due to the current in the coil.

Enclosure

• All components of the coil are enclosed in a protective casing.
• The pointer and scale are behind a glass cover.

The moving coil galvanometer works on the principle of the Lorentz force law. According to this law, when we place a current-carrying coil in the magnetic field, it will experience a torque. This torque will make the coil rotate, and the rotation is used to measure the current.

The torque is given by:  

τ=NIABsinθ

Where, 

• 'N' is the number of turns 
• B is the magnetic field strength 
• 'I' is current in the coil 
• 'A' area of the coil 
• θ angle between coil and field 

Important Links:

NCERT Class 11 notes	NCERT Class 11 Physics notes
Class 11 Chemistry Notes	Maths Class 11 NCERT Notes

The application of the moving coil galvanometer includes: 

1. Detection of Small Currents:

• Its main use is to detect the presence and direction of the current in the circuit. 

• A minute current produces a visible deflection on the scale. 

2. Measurement of Current:

• Can measure small direct currents accurately 

3. Conversion into an Ammeter:

• Connecting a low-resistance shunt in parallel to a galvanometer can convert it into an ammeter. 

4. Conversion into a Voltmeter:

• To convert a galvanometer into a voltmeter, we connect a high resistance in series with the coil.

5. Used in Bridge Circuits:

• Used in Wheatstone bridge and potentiometer experiments to detect null points.

Advantages of Moving Coil Galvanometer

• A galvanometer can detect small current
• The deflection in the galvanometer is directly proportional to the current.
• A galvanometer requires a small amount of current to operate.
• It gives accurate reading for direct current.

Disadvantage of Moving Coil Galvanometer

• It can not measure alternating current (AC) directly.
• The coil and suspension used in a galvanometer are sensitive and can be damaged easily.
• They are costly compared to simpler instruments.
• Temperature can change the resistance of the coil.

Here we have provided the complete notes for NCERT Class 12 Physics.

Sl. No	Name of Chapter
1	Chapter 1: Electric Charges and Fields
2	Chapter 2: Electrostatic Potential and Capacitance
3	Chapter 3: Current Electricity
4	Chapter 4: Moving Charges and Magnetism
5	Chapter 5: Magnetism and Matter
6	Chapter 6: Electromagnetic Induction
7	Chapter 7: Alternating Current
8	Chapter 8: Electromagnetic Waves
9	Chapter 9: Ray Optics and Optical Instruments
10	Chapter 10: Wave Optics
11	Chapter 11: Dual Nature of Radiation and Matter
12	Chapter 12: Atoms
13	Chapter 13: Nuclei
14	Chapter 14: Semiconductor Electronics: Materials, Devices and Simple Circuits

Students can find here the solutions for the Class 12 Physics exercise problems and practice questions.

Sl. No	Name of Chapter
1	Chapter 1 Electric Charges and Fields
2	Chapter 2 Electrostatic Potential and Capacitance
3	Chapter 3 Current Electricity
4	Chapter 4 Moving Charges and Magnetism
5	Chapter 5 Magnetism and Matter
6	Chapter 6 Electromagnetic Induction
7	Chapter 7 Alternating Current
8	Chapter 8 Electromagnetic Waves
9	Chapter 9 Ray Optics and Optical Instruments
10	Chapter 10 Wave Optics
11	Chapter 11 Dual Nature of Radiation and Matter
12	Chapter 12 Atoms
13	Chapter 13 Nuclei
14	Chapter 14 Semiconductor Electronics: Materials, Devices and Simple Circuits