Two long straight parallel wires are separated by a distance $2d$. Each wire carries a current $I$ in the same direction. The magnetic field at a point $P$ midway between them is

$A$ particle carrying a charge equal to $100$ times the charge on an electron is rotating one rotation per second in a circular path of radius $0.8 \ m$. The value of magnetic field produced at the centre will be $(\mu_0 = \text{permeability of vacuum})$

An electric current passes through a long straight wire. At a distance $5 \ cm$ from the wire,the magnetic field is $B$. The magnetic field at $20 \ cm$ from the wire would be:

$A$ long straight wire carries a current along the $x$-axis. Consider the points $A(0, 1, 0)$,$B(0, 1, 1)$,$C(1, 0, 1)$,and $D(1, 1, 1)$. Which of the following pairs of points will have magnetic fields of the same magnitude?

Two identical wires $A$ and $B$,each of length $l$,carry the same current $I$. Wire $A$ is bent into a circle of radius $R$ and wire $B$ is bent to form a square of side $a$. If $B_A$ and $B_B$ are the values of magnetic field at the centres of the circle and square respectively,then the ratio $\frac{B_A}{B_B}$ is

What is the ratio of the magnetic field at point $O$ in the given figures?