Two short bar magnets of length 1 cm each have magnetic moments 1.20 Am^{2} and 1.00 Am^{2} 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/m^{2})
3.6 x10^{-5} Wb/m^{2}
2.56 x10^{-4} Wb/m^{2}
3.50 x10^{-4} Wb/m^{2}
3.50 x10^{-4} Wb/m^{2}
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 N_{1}, N_{2} and N_{3} 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 N_{1} and N_{2} strongly but repel N_{3}
attract N_{1} strongly, N_{2} weakly and repel N_{3} weakly
attract N_{1} strongly, N_{2} weakly and repel N_{3} weakly
C.
attract N_{1} strongly, N_{2} weakly and repel N_{3} weakly
Two long conductors, separated by a distance d carry current I_{1} and I_{2} 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 m^{2} placed in a vibration magnetometer and oscillating in a uniform magnetic field 16π^{2} × 10^{-5} T makes 20 oscillations in 15 s. The magnetic moment of the bar magnet is
3 A-m^{2}
2 A-m^{2}
4 A-m^{2}
6 A-m^{2}
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