Two infinitely long insulated wires are kept perpendicular to each other. They carry currents $I_1=2 A$ and $I_2=1.5 A$. (i) Find the magnitude and direction of magnetic field at $P$. (ii) If the direction of the current is reversed in one of the wires, what would be the magnitude of the field $B$?

A long straight wire carrying a current of $200 A$ runs through a cubical box, entering and leaving through holes in the centres of opposite faces as shown in figure. Each side of the box is of $20 \mathrm{cm}$.

Consider an element $PQ$ of the wire $1 \mathrm{cm}$ long at the centre of the box. Calculate the magnetic field produced by this element at the point $A, B, C$ and $D$. The points $A, B$ and $C$ are the centres of the faces of the cube and $D$ is the midpoint of one edge.

Calculate the magnetic induction at the centre of a coil bent in the form of a square of side $10 \mathrm{cm}$10 cm carrying a current of $10 A$.

Two insulating infinitely long conductors carrying currents $I_1$ and $I_2$ lie mutually perpendicular to each other in the same plane as shown in figure. Find the magnetic field at point $P(a,b)$.