Magnetism and Matter

The magnetic susceptibility is negative for,

• a paramagnetic material only

• ferromagnetic material only

• paramagnetic and ferromagnetic materials

• paramagnetic and ferromagnetic materials

A wire carrying current I has the shape as shown in the adjoining figure. Linear parts of the wire are very long and parallel to X  -axis while semicircular portion of radius R is lying in a Y-Z plane. The magnetic field at point  O is.

A compass needle which is allowed to move in a horizontal plane is taken to a geomagnetic pole. it

• will become rigid showing no movement

• will stay in any position

• will stay in the north-south direction only

• will stay in the north-south direction only

Following figures show the arrangement of bar magnets in different configurations. Each magnet has magnetic dipole moments m. Which configuration has highest net magnetic dipole moment? 

Two identical long conducting wire AOB and COD are placed at right angle to each other, with one above other such that O is their common point for the two. The wires carry I₁ and I₂ currents, respectively. point P is lying at distance d from O along a direction perpendicular to the plane containing the wires. The magnetic field at the point P will be,

A bar magnet of length l and magnetic dipole moment M is bent in the form of an arc as shown in figure, The new magnetic dipole moment will be

• M

• 3M/π

• 2M/π

• 2M/π

There are four light -weight rod samples A, B, C D separately suspended by threads. A bar magnet is slowly brought near each sample and the following observations are noted

(i)  A is feebly repelled

(ii) B is feebly attracted

(iii) C is strongly attracted

(iv) D remains unaffected

• C is a diamagnetic material

• D is of a ferromagnetic material

• A is of a non- magnetic material

• A is of a non- magnetic material

A thin ring of radius R metre has charge q column uniformly spread on it. The ring rotates about its axis with a constant frequency of  f revolution/s. The value of magnetic induction in Wb m^-2 at the centre of the ring is

• μ_oq f/ 2π R

• μ_oq / f 2π R

• μ_oq / 2 f R

• μ_oq / 2 f R

Electromagnets are made of soft iron because soft iron has

• low retenitivity and high coercive force

• high retentivity and high coercive force

• low retentivity and low coercive force

• low retentivity and low coercive force

A vibration magnetometer placed in magnetic meridian has a small bar magnet. The magnet executes oscillations with a time period of 2s in earth's horizontal magnetic field of 24 μT. When a horizontal field of 18 μT is produced opposite to the earth's field by placing a current-carrying wire, the new time period of magnet will be

• 1s

• 2s

• 3s

• 3s