Question

The deflection in a moving coil galvanometer is
A. Deflection proportional to the torsional constant
B. Directly proportional to the number of turns in the coil
C. Inversely proportional to the area of the coil
D. Inversely proportional to the current flowing

Answer 1

Hint: To find out the correct option, recall the formula for the angular deflection of a moving coil galvanometer. Then see the dependency of the given quantities with the angular deflection of the moving coil galvanometer. Observe whether the quantities are directly or inversely proportional to angular deflection.

Complete step by step answer:
 The deflection in the moving coil galvanometer is given by the formula,
\[\phi = \left( {\dfrac{{NAB}}{k}} \right)I\]
Here, \[\phi \] is the angular deflection of the galvanometer,
\[I\] is the current flowing,
\[N\] is the number of turns in the coil,
\[A\] is the area of the coil,
\[B\] is the magnetic field and
\[k\] is the torsional constant

Now, comparing the options with the formula we have,
Option (a) is incorrect as torsional constant is inversely proportional to angular deflection not directly proportional.
Option (c) is incorrect as area of the coil is directly proportional to angular deflection not inversely proportional.
Option (d) is incorrect as current through the coil is directly proportional to angular deflection not inversely proportional
Option (b) is the correct option as number of turns in the coil is directly proportional to angular deflection.

So, the correct answer is “Option B”.

Note:
A moving coil galvanometer is an electromagnetic device which is used to measure small electric currents. The galvanometer consists of a coil having many turns and this coil is free to rotate about a fixed axis. When current flows through the coil and the device is placed in a uniform magnetic field then this current carrying coil experiences a torque and rotates about the fixed axis. This deflection indicates the presence and deflection of current.