Moving Coil Galvanometer: Principle, Construction, Theory, Galvanometer Constant, Sensitivity of Galvanometer

 Moving Coil Galvanometer

A moving coil galvanometer is an electromagnetic device that measures the electric current. It consists of a current-carrying coil placed in a magnetic field. When the current flows through the coil, it experiences torque, which causes the coil to rotate. The deflection of the coil is directly proportional to the strength of the current flowing through it.

⇒ Principle:

• The principle of a moving coil galvanometer is based on the torque on a current-carrying coil placed in a magnetic field.
• Torque acts on the coil due to the interaction between the magnetic field and the current-carrying wire.
• The deflection of the coil is directly proportional to the strength of the current flowing through it.

⇒ Construction:

• A moving coil galvanometer consists of a rectangular coil of wire, suspended by a thin wire or torsion fiber.
• The coil is placed in a magnetic field, created by a permanent magnet or an electromagnet.
• The coil is attached to a thin pointer, which moves along a calibrated scale.
• The scale is marked in units of current or voltage, depending on the application.
• A damping mechanism, such as air resistance, is used to reduce the oscillations of the pointer.

⇒ Theory:

• The torque on the coil is given by the product of the magnetic field, the current, and the area of the coil.
• The torque is proportional to the sine of the angle between the magnetic field and the plane of the coil.
• The restoring torque of the suspension wire or fiber is proportional to the angular displacement of the coil from its equilibrium position.
• The deflection of the coil is directly proportional to the current flowing through it.

⇒ Galvanometer Constant:

• The galvanometer constant is the current required to produce a unit deflection of the pointer.
• It is given by the ratio of the torque acting on the coil to the restoring torque of the suspension wire or fiber.
• It depends on the number of turns in the coil, the magnetic field strength, the area of the coil, and the torsion constant of the suspension wire or fiber.

⇒ Sensitivity of Galvanometer:

• The sensitivity of a galvanometer is the ratio of the change in the galvanometer reading to the change in the current or voltage being measured.
• It depends on the galvanometer constant and the damping mechanism used.
• The sensitivity can be increased by increasing the number of turns in the coil, the magnetic field strength, the area of the coil, and the torsion constant of the suspension wire or fiber.

In summary, a moving coil galvanometer works on the principle of torque on a current-carrying coil in a magnetic field. Its construction consists of a rectangular coil of wire suspended by a thin wire or torsion fiber, placed in a magnetic field created by a permanent magnet or an electromagnet. The theory of a moving coil galvanometer is based on the torque on the coil and the restoring torque of the suspension wire or fiber. The galvanometer constant is the current required to produce a unit deflection of the pointer and depends on several factors. The sensitivity of a galvanometer is the ratio of the change in the galvanometer reading to the change in the current or voltage being measured and can be increased by various means.  

Frequently Asked Questions – FAQs

⇒ What is the principle of a Moving Coil Galvanometer?

The working principle of a Moving Coil Galvanometer is that when a current-carrying coil is placed in a magnetic field, it experiences a torque. Under the action of this torque, the coil rotates and the deflection in the coil in a Moving Coil Galvanometer is directly proportional to the current flowing through the coil.

⇒ What is the construction of a Suspended Type Moving Coil Galvanometer?

A Suspended Type Moving Coil Galvanometer consists of a rectangular coil PQRS of insulated thin copper wire, a soft iron cylindrical core, a spring, and a pointer. The field is made radial and strong with the help of a soft iron cylindrical core.

⇒ What is the theory behind the Moving Coil Galvanometer?

The theory behind the Moving Coil Galvanometer is that a current-carrying coil experiences torque when placed in a magnetic field. As the electric current is passed through the coil, a torque acts on it, which deflects the coil. The deflection of the coil is measured using a scale, and the magnitude of the current can be calculated.

⇒ What is the galvanometer constant?

The galvanometer constant is defined as the current required to produce unit deflection in the Moving Coil Galvanometer. It is denoted by 'K' and is given by the expression K = θ/I where θ is the deflection produced in the galvanometer and I is the current flowing through the galvanometer.

⇒ What is the sensitivity of a Moving Coil Galvanometer?

The sensitivity of a Moving Coil Galvanometer is defined as the deflection produced by a unit current. It is denoted by S and is given by the expression S = K/R where R is the resistance of the galvanometer.

⇒ What are the different types of Moving Coil Galvanometer?

Moving Coil Galvanometers are mainly divided into two types: Suspended coil galvanometer and Pivoted-coil or Weston galvanometer.

⇒ What is the torsional constant of the suspension wire?

The torsional constant of the suspension wire is a measure of the resistance of the wire to twisting. It is denoted by 'C' and is given by the expression C = 2πnD^4/32L where n is the number of turns in the wire, D is the diameter of the wire, and L is the length of the wire.

⇒ How does a Moving Coil Galvanometer work?

A Moving Coil Galvanometer works on the principle that a current-carrying coil experiences torque when placed in a magnetic field. As the electric current is passed through the coil, a torque acts on it, which deflects the coil. The deflection of the coil is measured using a scale, and the magnitude of the current can be calculated.

⇒ What are the different parts of a Moving Coil Galvanometer?

The different parts of a Moving Coil Galvanometer are Horseshoe magnet, Coil, Spring, and Pointer.

⇒ What are the current and voltage sensitivity of a Moving Coil Galvanometer?

The current sensitivity of a Moving Coil Galvanometer is the deflection produced by a unit current. The voltage sensitivity is the deflection produced by a unit voltage.

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