Question

In a moving coil galvanometer, the magnetic pole pieces are made cylindrical and soft iron core is placed at the centre of the coil, the purpose of doing so is:
(A) To make the magnetic field strong
(B) To make the magnetic field strong and radial
(C) To make the magnetic field uniform
(D) To make the magnetic field strong and uniform

Answer 1

Hint:We have to first know that a moving coil galvanometer is nothing but a very sensitive ammeter. It detects very small currents in circuits. Now, since we already know the constructions and materials present in a moving coil galvanometer, we have to associate it with the nature of the magnetic field produced in the moving coil galvanometer.

Step by step solution:
In a moving coil galvanometer, the magnetic pole pieces are usually constructed cylindrical and the soft iron core is placed at the centre of the coil. The sole purpose of doing so is to ensure that the magnetic field produced in the moving coil galvanometer is strong and also radial. The magnetic field inside the moving coil galvanometer is kept strong so that even when a very small electric field is detected, the needle of the moving coil galvanometer shows a deflection. The radial magnetic field produced in the moving coil galvanometer is applied to produce a constant torque in the needle of the galvanometer. Hence, the correct option for this question is (B).

Note:The soft iron core used in a moving coil galvanometer is ferromagnetic in nature. This ensures that the magnetic field lines produced in the core are increased and as a result the sensitivity of the moving coil galvanometer is also increased. If the magnetic field inside a moving coil galvanometer were kept uniform, the torque experienced by the needle would be very less and as a result the sensitivity of the galvanometer would decrease.