Moving Coil Galvanometer

Basic principle and construction:

• A moving coil galvanometer consists of a coil of wire suspended between the poles of a permanent magnet.
• When a current flows through the coil, it creates a magnetic field that interacts with the magnetic field of the permanent magnet, causing the coil to rotate.

Controlling torque:

• The controlling torque in a moving coil galvanometer is provided by a spring attached to the coil. The spring opposes the rotation of the coil, providing a restoring force.

Current sensitivity and voltage sensitivity:

• The current sensitivity of a moving coil galvanometer is defined as the deflection produced by a current of one ampere. The voltage sensitivity is the deflection produced by a voltage of one volt.

Conversion to ammeter and voltmeter:

• A moving coil galvanometer can be converted into an ammeter by connecting a shunt resistor in parallel with the coil.
• To convert it into a voltmeter, a series resistor is connected in series with the coil.

Shunts and multipliers:

• Shunts and multipliers are used to extend the range of a moving coil galvanometer. A shunt is a low-resistance resistor connected in parallel with the coil, while a multiplier is a high-resistance resistor connected in series with the coil.

Potential Energy of a Dipole

Expression for potential energy:

• The potential energy of a dipole in an electric field can be expressed as: $$U = - \vec{p} \cdot \vec{E}$$

where is the dipole moment, is the electric field, and is the angle between the dipole moment and the electric field.

Dipole in a uniform electric field:

• In a uniform electric field, the potential energy of a dipole is given by: $$U = - pE \cos\theta$$

Torque on a dipole in a uniform electric field:

• The torque acting on a dipole in a uniform electric field is given by: $$\vec{\tau} = \vec{p} \times \vec{E}$$

Potential energy of a dipole in a non-uniform electric field:

• The potential energy of a dipole in a non-uniform electric field can be expressed as: $$U = -\int\vec{p}\cdot d\vec{E}$$

Additional Concepts

Ballistic galvanometer:

A ballistic galvanometer is a moving coil galvanometer that is used to measure the total charge passed through it.

Sensitivity of a galvanometer:

The sensitivity of a galvanometer is defined as the deflection produced by a specific current or voltage.

Resolution of a galvanometer:

The resolution of a galvanometer is defined as the smallest change in current or voltage that can be detected by the galvanometer.

Potentiometer:

A potentiometer is a device that can be used to measure an unknown voltage by comparing it to a known voltage.

Voltmeter with infinite resistance:

A voltmeter with infinite resistance is a voltmeter that does not draw any current from the circuit being measured.