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 in the horizontal plane carries a current of $50 \; A$ in the north to south direction. Give the magnitude and direction of $B$ at a point $2.5 \; m$ east of the wire.

The electric current in a circular coil of $2$ turns produces a magnetic induction $B_{1}$ at its centre. The coil is unwound and is rewound into a circular coil of $5$ turns and the same current produces a magnetic induction $B_{2}$ at its centre. The ratio of $\frac{B_{2}}{B_{1}}$ is:

Two infinitely long wires, each carrying a current $I = 10 \ A$, are bent to form a right angle as shown in the figure. Find the magnetic induction at point $O$. $\left[\mu_0 = 4\pi \times 10^{-7} \ H \ m^{-1}\right]$

$A$ cylindrical conductor of radius $R$ carries a current $i$. The value of the magnetic field at a point which is $R/4$ distance inside from the surface is $10 \, T$. Find the value of the magnetic field at a point which is $4R$ distance outside from the surface.

The current passing through a conducting loop in the form of an equilateral triangle of side $4\sqrt{3} \text{ cm}$ is $2 \text{ A}$. The magnetic field at its centroid is $\alpha \times 10^{-5} \text{ T}$. The value of $\alpha$ is . . . . . . . (Given: $\mu_0 = 4\pi \times 10^{-7} \text{ SI units}$)