Explanation
We know that at magnetic poles the horizontal component of earth’s field is zero, only vertical component exists.
So, as compass needle is free to rotate in horizontal plane and is thus effected by horizontal component only as H = 0, hence, compass needle may stay in any direction.
The dip needle rotates in a vertical plane and the angle of dip at poles is 900. Hence, the dip needle will stand vertical at the north pole of earth.
The earth has only vertical component of its magnetic field at the magnetic poles. Since compass needle is only free to rotate in horizontal plane, at north pole the vertical component of earth’s field will exert torque on the magnetic needle so as to align it along its direction. As the compass needle can not rotate in vertical plane, it will rest horizontally when placed on the magnetic pole of the earth.
We observe that both the magnets exert equal and opposite force/torque on each other. Hence, net force/torque on cork will be zero.
The susceptibility of ferromagnetic substance of decreases with the rise of temperature in a complicated manner. After Curie point the susceptibility of ferromagnetic substance varies inversely with its absolute temperature, Ferromagnetic substance obey’s Curie’s law only above its Curie point.
The properties of a substance is due to alignment of molecules in it. When these substances are heated, molecules acquire some kinetic energy. some of the molecules may get back to the closed chain arrangement (leading to zero resultant). So they lose their magnetic property or magnetism. Therefore the properties of both ferromagnetic and paramagnetic are effected by heating.
The core of a transformer undergoes cycles of magnetisation again and again. During each cycle of magnetisation, energy numerically equal to the area of the hysteresis loop is spent per unit volume of the core. Therefore, for high efficiency of transformer, the energy loss will be lesser if the hysteresis 1oop is of lesser area, i. e., narrow. That’s why soft iron is used as core, which has narrow hysteresis loop (or area of B-H curve is very small). Also soft iron (ferromagnetic substance) has high permeability, high retentivity, low coercivity and low hysteresis loss.
A magnetic field is produced by the motion of electric charge. Since motion is relative, the magnetic field is also relative.
In a moving coil galvonometer, the coil is suspended in a very strong uniform magnetic field created by two magnetic pole pieces. The earth’s magnetic field is quite weak as compared to that field, therefore, it does not affect the working of magnetic field.
Diamagnetic materials, when placed in magnetic field are oppositely magnetised.
Steel is preferred over soft iron for making permanent magnets because coercivity of steel is larger.
In general, the field due to a magnet is non-uniform. Therefore, it exerts both force and torque on the nails which will translate and also rotate the nails before striking to north pole of magnet with their induced south poles and vice-versa.
In a non-uniform magnetic field, both torque and net force acts on the dipole. If magnetic field were uniform, net force on dipole would be zero.
A paramagnetic sample displays greater magnetization when cooled, this is because at lower temperature, the tendency to disrupt the alignment of dipoles (due to magnetising field) decreases on account of reduced random thermal motion.
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