In the previous question,if the current is $i$ and the magnetic field at $D$ has magnitude $B$,

$A$ particle having a charge $100 e$ is revolving in a circular path of radius $0.8 \ m$ with $1 \ r.p.s$. The magnetic field produced at the center of the circle in $SI$ unit is ($\mu_0$ is the permeability of vacuum,$e = 1.6 \times 10^{-19} \ C$).

$A$ current $I$ flows in an anticlockwise direction in a circular arc of a wire having $\left(\frac{3}{4}\right)^{\text{th}}$ of the circumference of a circle of radius $R$. The magnetic field $B$ at the centre of the circle is $(\mu_0 = \text{permeability of free space})$

Two long parallel wires are separated by a distance of $2.50 \ cm$. The force per unit length that each wire exerts on the other is $4 \times 10^{-5} \ N \ m^{-1}$, and the wires repel each other. The current in one wire is $0.5 \ A$. What is the current in the second wire (in $A$)? (Take $\mu_0 = 4 \pi \times 10^{-7} \ S.I. \ \text{unit}$)

$A$ current of $I$ $A$ is passed through a straight wire of length $2.0$ $m$. The magnetic field at a point in air at a distance of $3$ $m$ from either end of the wire and lying on the axis of the wire will be:

$A$ current $I$ flows in an infinitely long wire with a cross-section in the form of a semi-circular ring of radius $R$. The magnitude of the magnetic induction along its axis is: