A current $I$ flows in a long straight wire with cross-section having the form of a thin half-ring of radius $R$. Find the induction of the magnetic field at the point $O$. 

Find the magnetic induction at the point $O$, if the wire carrying a current $I=8.0 \mathrm{A}$ has the shape shown in the figure.

The radius of the curved part of the wire is $R=100 \mathrm{mm}$, the linear parts of the wire are very long

In the figure two long straight wires are perpendicular to the page and separated by distance $d_1=0.75 \mathrm{cm}.$ Wire $1$ carries $6.5 \mathrm{A}$ into the page. What are the 

(a) magnitude and 

(b) direction (into or out of the page) of the current in wire $2$ if the net magnetic field due to the two currents is zero at point $P$ located at distance $d_2=2.50 \mathrm{cm}$ from wire $2$? If the current in wire $2$ is then reversed, what will be the 

(c) magnitude and 

(d) direction of the net field at point $P ?$ 

A circular loop of radius $4.0 \mathrm{cm}$ is placed in a horizontal plane and carries an electric current of $5.0 \mathrm{A}$ in the clockwise direction as seen from above. Find the magnetic field (a) at a point $3.0 \mathrm{cm}$ above the centre of the loop (b) at a point $3.0 \mathrm{cm}$ below the centre of the loop.