Torque

The magnet in a magnetic field experiences a torque which rotates the magnet to a position in which the axis of the magnet is parallel to the field.

%5Ctau%20%3DMB%5Ctext%7B%20%7Dsin%5C%2C%5Ctheta

where,

M

is magnetic dipole moment,

B

the magnetic field and

%5Ctheta

the angle between the two.
Given,

%7B%7B%5Ctau%20%7D_%7B1%7D%7D%3D%7B%7B10%7D%5E%7B-5%7D%7DNm%2C%7B%7B%5Ctheta%20%7D_%7B1%7D%7D%3D90%7B%7D%5E%5Ccirc%20%2C%7B%7B%5Ctheta%20%7D_%7B2%7D%7D%3D30%7B%7D%5E%5Ccirc%20%2C

%7B%7B%5Ctau%20%7D_%7B1%7D%7D%3DMB%5Csin%2090%7B%7D%5E%5Ccirc

...(i)

%7B%7B%5Ctau%20%7D_%7B2%7D%7D%3DMB%5Csin%2030%7B%7D%5E%5Ccirc

...(ii)
Dividing E (i) by E i(ii), we get

%5Cfrac%7B%7B%7B%5Ctau%20%7D_%7B1%7D%7D%7D%7B%7B%7B%5Ctau%20%7D_%7B2%7D%7D%7D%3D%5Cfrac%7B%7B%7B10%7D%5E%7B-5%7D%7D%7D%7B%7B%7B%5Ctau%20%7D_%7B2%7D%7D%7D%3D%5Cfrac%7B1%7D%7B1%2F2%7D

%5CRightarrow

%7B%7B%5Ctau%20%7D_%7B2%7D%7D%3D%5Cfrac%7B%7B%7B10%7D%5E%7B-5%7D%7D%7D%7B2%7D

%3D%5Cfrac%7B10%7D%7B2%7D%5Ctimes%20%7B%7B10%7D%5E%7B-6%7D%7D

%3D5%5Ctimes%20%7B%7B10%7D%5E%7B-6%7D%7DNm

Chapter Questions
1 MCQs