Question

What is the shape of a magnet in a moving coil galvanometer to make the radial magnetic field?
A. Concave
B. Horseshoe magnet
C. Convex
D. None of the above

Answer 1

Hint: The construction of the moving coil galvanometer is the topic of concept that we will use in this question. To improve the device's distinctive traits, some features are added. The solution is connected to how the moving coil galvanometer operates since only then will we be able to understand why the magnetic field is radial in it and how to use it. This is one way to solve the question.

Complete step by step solution:
Principle: A moving coil galvanometer works on the theory that a coil carrying current experiences a torque when it is placed in a magnetic field.

Construction: The illustration depicts a moving coil ballistic galvanometer.



It essentially consists of a PQRS coil wound around a non-conducting frame made of ivory or bamboo, which can be either rectangular or cylindrical. Between the pole components of a strong horseshoe magnet, NS, this coil is strung by phosphor bronze wire. The magnet's poles are bent to create a radial field.

A spring made of phosphor-bronze wire is affixed to the coil's lower end. On the top of the instrument's case, two terminals $T_2$ and $T_1$ are connected to the spring and the free ends of phosphor bronze wire, respectively. The suspension wire is fastened with a tiny mirror M.

It is possible to record the coil's deflection using a lamp and scale configuration. A non-metallic container encloses the entire setup. Concave magnets are the shape of the magnet used in moving coil galvanometers to create the radial magnetic field.

Hence, option A is the correct answer.

Note: A moving coil galvanometer, which measures extremely low current levels expressed in terms of microamperes, is a very delicate instrument. By measuring the coil's deflection, one can estimate the amount of current flowing through it. This is caused due to the torque that acts on it. In other words, the relationship between the current and deflection angle is linear.