Current I is flowing in conductor shaped as shown in the figure, Fig.$8.121.$ The radius of the curved path is $r$ and the length of the straight portion is very large. The value of the magnetic field at the centre $O$ will be 

 

A current I enters a circular coil of radius $R,$ branches into two parts and then recombines as shown in figure, Fig.$8.122.$ The resultant magnetic field at the centre of the coil is 

A part of long wire carrying a current $\mathfrak{i}$ is bent into a circle of radius $r$ as shown in figure, Fig.$8.123.$ The net magnetic field at the centre $O$ of the circular loop is 

A current $\mathfrak{i}$ is flowing through the loop. The direction of the current and the shape of the loop are as shown in figure, Fig.$8.124.$ The magnetic field at the centre of the loop is $\frac{{\mu }_0\mathfrak{i}}{R}$ times $\left(MA=R, MB=2R, \angle DMA=90°\right)$

Current through $ABC$ and $A\text{'}B\text{'}C\text{'}$ is $I$ Fig $8.125$. What is the magnetic field at $P$? $BP=PB\text{'}=r$ ( Here $C\text{'}B\text{'}PBC$ are collinear)