Magnetism and Matter

Two short bar magnets of length 1 cm each have magnetic moments 1.20 Am² and 1.00 Am² respectively. They are placed on a horizontal table parallel to each other with their N poles pointing towards the South.
They have a common magnetic equator and are separated by a distance of 20.0 cm. The value of the resultant horizontal magnetic induction at the mid - point O of the line joining their centres is close to(Horizontal component of earth’s magnetic induction is 3.6 × 10–5 Wb/m²)

• 3.6 x10^-5 Wb/m²

• 2.56 x10^-4 Wb/m²

• 3.50  x10^-4 Wb/m²

• 3.50  x10^-4 Wb/m²

Relative permittivity and permeability of a material are ε_r and µ_r, respectively. Which of the following values of these quantities are allowed for a diamagnetic material?

• ε_r = 0.5, µ_r = 1.5

• ε_r = 1.5, µ_r = 0.5

• ε_r = 0.5, µr = 0.5

• ε_r = 0.5, µr = 0.5

Needles N₁, N₂ and N₃ are made of a ferromagnetic, a paramagnetic and a diamagnetic substance respectively. A magnet when brought close to them will

• attract all three of them

• attract N₁ and N₂ strongly but repel N₃

• attract N₁ strongly, N₂ weakly and repel N₃ weakly

• attract N₁ strongly, N₂ weakly and repel N₃ weakly

Two long conductors, separated by a distance d carry current I₁ and I₂ in the same direction. They exert a force F on each other. Now the current in one of them increased to two times and its direction reversed. The distance is also increased to 3d. The new value of the force between them is

• −2F 

• F/3

• −2F/3

• −2F/3

The length of a magnet is large compared to its width and breadth. The time period of its width and breadth. The time period of its oscillation in a vibration magnetometer is 2 s. The magnet is cut along its length into three equal parts and three parts are then placed on each other with their like poles together. The time period of this combination will be

• 2 s

• 2/3 s

• 2√3 s

• 2√3 s

The materials suitable for making electromagnets should have

• high retentivity and high coercivity

• low retentivity and low coercivity

• high retentivity and low coercivity

• high retentivity and low coercivity

A bar magnet of moment of inertia 9 x 10^-5 kg m² placed in a vibration magnetometer and oscillating in a uniform magnetic field 16π² × 10^-5 T makes 20 oscillations in 15 s. The magnetic moment of the bar magnet is

• 3 A-m²

• 2 A-m²

• 4 A-m²

• 6 A-m²

Identify the correctly matched pair

• Diamagnetic   —   Gadolinium

• Soft ferromagnetic   —   Alnico

• Hard ferromagnetic   —   Copper

• Paramagnetic   —   Sodium

The ferromagnetic core of electromagnets should have

• a broad hysteresis loop

• high permeability and high retentivity

• high permeability and low retentivity

• low permeability and high retentivity

A metal conductor of length 1 m rotates vertically about one of its ends at angular velocity 5 rads^-1. If the horizontal component of earth's magnetic field is 0.2 x 10^-4 T, then the emf developed between the ends of the conductor is

• 5 µV

• 5 mV

• 50 µV

• 50 mV