Question

Assertion (A): The cylindrical soft iron core in a moving coil galvanometer only makes the magnetic field radial and does not affect the strength of the magnetic field.

Reason (R): In a moving coil galvanometer, the plane of the coil is always perpendicular to the magnetic field.

Options

• Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

• Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).

• Assertion (A) is true, but Reason (R) is false.

• Both Assertion (A) and Reason (R) are false.

Answer 1

Both Assertion (A) and Reason (R) are false.

Explanation:

In a moving coil galvanometer:

• A cylindrical soft iron core is placed inside the coil.
• It produces a strong radial magnetic field.

Analyze Assertion

The soft iron core:

• Makes the magnetic field radial (true).
• Also increases the magnetic field strength because of its high permeability.

Therefore, the statement that it does not affect the strength of the magnetic field is incorrect.

Hence, Assertion (A) is false.

Analyze Reason

In a radial magnetic field:

τ = nBI A sin⁡ θ

Since the field is radial, the plane of the coil remains parallel to the magnetic field lines. As a result, the normal to the coil stays perpendicular to the field, giving constant torque.

Thus, the given statement in the reason is incorrect.

Hence, Reason (R) is false.