A current ampere flows along an infinitely long straight thin walled tube, then the magnetic induction at any point inside the tube is
A long wire carries a steady current. It is bent into a circle of one turn and the magnetic field at the centre of the coil is B It is then bent into a circular loop of n turns. The magnetic field at the centre of the coil will be
The magnetic field due to a current carrying circular loop of radius 3 cm at a point on the axis at a distance of 4 cm from the centre is . What will be its value at the centre of the loop ?
Two long conductors, separated by a distance d carry current in the same direction .They exert a force F on each other Now the current in one of them is increased to two times and its direction is reversed. The distance is also increased to 3d . The new value of the force between them is
The length of a magnet is large compared to 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
The materials suitable for making electromagnets should have
high retentivity and high coercivity
low retentivity and low coercivity
high retentivity and low coercivity
low retentivity and high coercivity.