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# Physics Project On Moving Coil Galva

## Physics Project on Moving Coil Galvanometer

A moving coil galvanometer is a device that can measure small electric currents by converting them into angular deflections of a coil in a magnetic field. In this article, we will learn about the working principle, construction, and applications of a moving coil galvanometer. We will also see how to convert a galvanometer into an ammeter or a voltmeter.

## Working Principle of Moving Coil Galvanometer

A moving coil galvanometer works on the principle that a current-carrying coil placed in a magnetic field experiences a torque. The torque is proportional to the product of the current, the magnetic field, and the sine of the angle between the coil and the field. The torque causes the coil to rotate until it is balanced by a restoring torque provided by a spring attached to the coil. The angular deflection of the coil is proportional to the current flowing through it.

## Construction of Moving Coil Galvanometer

A typical moving coil galvanometer consists of the following components:

• A rectangular coil of thin insulated copper wire with a large number of turns. The coil is wound on a cylindrical core made of soft iron, which enhances the magnetic field inside the coil.

• A permanent magnet with concave pole pieces, which produces a radial magnetic field in the region where the coil is placed. The radial field ensures that the angle between the coil and the field remains constant at 90 degrees, regardless of the orientation of the coil.

• A pair of coil springs, which are attached to the ends of the coil and provide a restoring torque that opposes the rotation of the coil. The springs also serve as electrical contacts for connecting the coil to an external circuit.

• A pointer, which is fixed to the coil and moves along a calibrated scale to indicate the deflection of the coil.

## Applications of Moving Coil Galvanometer

A moving coil galvanometer can be used for various purposes, such as:

• Measuring small electric currents in circuits or devices.

• Detecting the presence or direction of electric currents or magnetic fields.

• Studying the properties of electromagnetic induction or electromagnetic waves.

• Converting into an ammeter or a voltmeter by adding suitable resistors in parallel or series with the galvanometer.

## Conversion of Galvanometer into Ammeter or Voltmeter

An ammeter is a device that measures electric current, while a voltmeter is a device that measures electric potential difference or voltage. A moving coil galvanometer can be converted into either an ammeter or a voltmeter by adding suitable resistors in parallel or series with it.

### Conversion into Ammeter

An ammeter should have a low resistance, so that it does not affect the current that it measures. To convert a galvanometer into an ammeter, we need to connect a low resistance resistor, called a shunt resistor, in parallel with the galvanometer. The shunt resistor allows most of the current to bypass the galvanometer, while only a small fraction passes through it. The value of the shunt resistor can be calculated using Kirchhoff's current law and Ohm's law.

### Conversion into Voltmeter

A voltmeter should have a high resistance, so that it does not draw any significant current from the circuit that it measures. To convert a galvanometer into a voltmeter, we need to connect a high resistance resistor, called a series resistor, in series with the galvanometer. The series resistor limits the current that flows through the galvanometer, while allowing it to measure the potential difference across its terminals. The value of the series resistor can be calculated using Kirchhoff's voltage law and Ohm's law.