Question

Describe the working principle of a moving coil galvanometer. Why is it necessary to use (i) a radial magnetic field and (ii) a cylindrical soft iron core in a galvanometer? Write the expression for current sensitivity of the galvanometer.
Can a galvanometer as such be used for measuring the current? Explain.

Answer 1

Answer:

Moving coil galvanometer is an instrument used for the detection and measurement of small currents. Principle: The working of moving coil galvanometer is that when a current carrying coil is placed in a varying magnetic field, it experiences torque. ... Also, it increases the strength of the magnetic field.

Answer 2

Galvanometer, its core, expression for current sensitivity and application

• When an electric current flows in a coil placed in a magnetic field, a deflecting torque acts upon the coil. The magnitude depends upon the strength of the current.
• A radial magnetic field is used to achieve a constant torque in the magnetic field irrespective of its rotation.    
• A cylindrical soft iron core is used to increase the sensitivity of the galvanometer as the iron core tends to concentrate the entire magnetic field through the core of the galvanometer, such that there are no losses in transmission.
• An expression for current sensitivity of the Galvanometer is given by the relation $I=\frac{k}{n A B}$∅ , where  ∅ is the Angle of Deflection, $n$ is the number of turns, $A$ is the Area, $B$ is the magnetic induction and $k$ is the Couples.
• The galvanometer cannot be used to measure current as such flowing in a circuit. It is used to detect the presence of current in a circuit and its subsequent direction.

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