Question

A magnetic needle is kept in a non-uniform magnetic field. It experiences
A. A force and a torque
B. A force but not a torque
C. A torque but not a force
D. Neither a force nor a torque

Answer 1

If the magnetic field will vary in its strength and direction at separate points then it is known as a non-uniform magnetic field. A bar magnet also yields a non-uniform magnetic field. It can be observed by the magnetic lines of force starting from the north pole of the magnet to the south pole of the magnet.

Complete step by step solution:
The magnetic needle is also generating a non-uniform magnetic field and, in this question, it is given that the magnetic needle is kept in a non-uniform magnetic field. In this case, the needle will experience a torque that will make it align with the region of the magnetic field of tougher strength in the total non-uniform magnetic field region. And this magnetic needle will not only experience the torque but a total force also and the direction of this force will be in the direction of the stronger region of the magnetic field. Therefore if a magnetic needle is located in a non-uniform magnetic field then it will undergo both torques as well as force.
So the correct answer is in option (B).
Note:
A magnetic needle is also known as a magnetic dipole. In a non-uniform Magnetic field, the force on each of the poles will be dissimilar in both magnitude and direction. Due to changes in Magnitude, the dipole undergoes a Force, Due to changes in direction the dipole undergoes a Torque. So, this torque will keep the needle aligned with the uniform magnetic field. A uniform magnetic field will have equal magnitude and direction all over its area.