Two infinitely long thin wires are placed at $(1 \mathrm{~cm}, 0 \mathrm{~cm})$ and $(2 \mathrm{~cm}, 0 \mathrm{~cm})$ as shown in the figure.

The same current $i$ flows in both the wires in the same direction, say, into the page. Let the magnetic field at the origin due to these wires is $\mathbf{B}$. If $B_0$ is the magnitude of the magnetic field, if only the wire at $(1 \mathrm{~cm}, 0 \mathrm{~cm})$ was present, then the value of $\frac{B}{B_0}$ is

A toroid core has inner radius of 0.24 m and outer radius of 0.26 m . A current of 10 A flows through the wire having 2500 turns around it. Find the magnetic field inside the core of the toroid

A current carrying loop $A B C D$ has two circular arcs $A D$ and $B C$ with radius 1 cm and 2 cm respectively, as shown in the figure. The two arcs $A D$ and $B C$ subtend a common angle $30^{\circ}$ at the centre $O$. If the current flowing in the loop is $\frac{12}{\pi} \mathrm{~A}$. Then, the magnitude of net magnetic field at $O$ is (given, $\mu_0=4 \pi \times 10^{-7}$ )

Three parallel wires $a, b$ and $c$ carrying currents $i_a, i_b$ and $i_c$ as shown in the figure are placed next to each other.

The magnitude force on a length $l$ of the wire $a$, if $d_2=2 d_1, i_b=i_a$ and $i_c=4 i_a$ is