A rectangular loop of sides 25 cm and 10 cm carrying a current of 10 A is placed with its longer side parallel to a long straight conductor 10 cm apart carrying current 25 A . The net force on the loop is

Two long straight parallel conductors $A$ and $B$ carrying currents 4.5 A and 8 A respectively, are separated by 25 cm in air. The resultant magnetic field at a point which is at a distance of 15 cm from conductor $A$ and 20 cm from conductor $B$ is

Two concentric thin circular rings of radii 50 cm and 40 cm , each carry a current of 3.5 A in opposite directions. If the two rings are coplanar, the net magnetic field due to the rings at their centre is

In hydrogen atom an electron is making $6.6 \times 10^{15} \mathrm{rev} / \mathrm{s}$ around the nucleus of radius $0.47 $$\mathop A\limits^o $. The magnetic field induction produced at the centre of the orbit is nearly.