# Test on magnetism--torque, work done on a dipole

A bar magnet of magnetic moment 200 A-m2 is suspended in a magnetic field of intensity 0.25 N/A-m. The couple required to deflect it through 30o is ____.
50 N-m
25 N-m
20 N-m
15 N-m
A bar magnet is held perpendicular to a uniform magnetic field. If the couple acting on the magnet is to be halved by rotating it, then the angle by which it is to be rotated is ____.
30o
45o
60o
90o
A bar magnet of magnetic moment 3.0 A-m2 is placed in a uniform magnetic induction field of 2 ( 10–5 T. If each pole of the magnet experiences a force of 6 ( 10–4 N, the length of the magnet is ____.
0.5 m
0.3 m
0.2 m
0.1 m
There is no couple acting when two bar magnets are placed coaxially separated by a distance because ____.
There are no forces on the poles
The forces are parallel and their lines of action do not coincide
The forces are perpendicular to each other
The forces act along the same line
If the magnetic flux is expressed in weber, then magnetic induction can be expressed in ____.
Weber/m2
Weber/m
Weber-m
Weber-m2
If a hole is made at the centre of a bar magnet, then its magnetic moment is ____.
Increase
Decrease
Not change
None of the above
The work done in turning a magnet of magnetic moment 'M' by an angle of 90° from the meridian is 'n' times the corresponding work done to turn it through an angle of 60°, where 'n' is given by ____.
1/2
2
1/4
1
A bar magnet of magnetic moment 104J/T is free to rotate in a horizontal plane. The work done in rotating the magnet slowly from a direction parallel to a horizontal magnetic field of 4×10–5 T to a direction 60° from the field is ____.
0.2 J
2.0 J
4.18 J
2 × 102 J
Two short magnets with their axes horizontal and perpendicular to the magnetic meridian are placed with their centres 40 cm east and 50 cm west of magnetic needle. If the needle remains undeflected, the ratio of their magnetic moments  is ____.
4 : 5
16 : 25
64 : 125
Description:

This test is based on torque on a dipole, work done in rotating a dipole etc

Discussion
Kajal Sengupta
Physics 9th to 12 th grade,CIE, Edexcel, AP, IB , CBSE, ICSE 87 Members Recommend
880 Followers