Question

In a moving coil galvanometer a radial magnetic field is applied with concave magnetic poles, to have
A) Uniform magnetic field
B) The plane of the coil parallel to field
Choose the correct option among the following
(A) Both A and B are true
(B) Both A and B are false
(C) A is true, B is false
(D) A is true, B is true

Answer 1

Hint: A moving coil galvanometer works on the principle that when a current carrying loop or coil is placed in the uniform magnetic field, it experiences a torque. Write the formula related to that and then relate. In the radial magnetic field, the plane of the coil in all positions is parallel to the direction of the magnetic field.

Complete solution:
In a moving coil galvanometer, a radial magnetic field is applied with concave magnetic poles in order to have a uniform magnetic field. As the magnetic field is radial, so the plane of the coil is parallel to the magnetic field such that the angle between the magnetic field and the plane of the coil becomes the right angle.
Formula is given by: ${{\tau = BINA sin \theta }}$
As $\theta = 90^\circ$
So, $ \tau = BINA sin 90^\circ$
$\therefore {{\tau = BINA}}$
Which implies that the plane of the coil is parallel to the field.
Thus, in a moving coil galvanometer a radial magnetic field is uniform magnetic field and the plane of the coil is parallel to the magnetic field.
So, both the statements (A) and (B) are true.

Therefore, option (A) is the correct choice.

Note: A radial magnetic field is produced by cylindrical poles of magnet (permanent magnet) of galvanometer is parallel to the coil. A moving coil galvanometer is an instrument which measures electric current. It is a very sensitive electromagnetic device that can measure the value of low currents even of the order of a few microamperes. However parallax error happens when the object is viewed from an angle because of the wrong position of the viewer’s eye due to this, a mirror is used for high precision of electrical quantity that measures instruments (particularly analog type).