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Multiple Choice QuestionsSeverity: Notice
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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
B.
low retentivity and low coercivity
Electromagnets are made of soft iron. The soft iron has high retentivity and low coercivity.
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
B.
2.56 x10-4 Wb/m2
Relative permittivity and permeability of a material are εr and µr, respectively. Which of the following values of these quantities are allowed for a diamagnetic material?
εr = 0.5, µr = 1.5
εr = 1.5, µr = 0.5
εr = 0.5, µr = 0.5
εr = 0.5, µr = 0.5
B.
εr = 1.5, µr = 0.5
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
C.
−2F/3
Force acting between two current carrying conductors
where d = distance between the conductors,
l = length of each conductor
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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
C.
attract N1 strongly, N2 weakly and repel N3 weakly
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
B.
2/3 s
The time period of oscillations of magnet
where I = moment of inertia of magnet = mL2/12 (m is being the mass of magnet)
M = pole strength × L When the three equal parts of magnet are placed on one another with their like poles together, then
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