Two parallel wires of equal lengths are separated by a distance of $$3 \mathrm{~m}$$ from each other. The currents flowing through $$1^{\text {st }}$$ and $$2^{\text {nd }}$$ wire is $$3 \mathrm{~A}$$ and 4.5 A respectively in opposite directions. The resultant magnetic field at mid point between the wires $$\left(\mu_0=\right.$$ permeability of free space)

An electron is projected along the axis of circular conductor carrying current I. Electron will experience

The magnetic field at the centre of a circular coil of radius '$$R$$', carrying current $$2 A$$ is '$$B_1$$'. The magnetic field at the centre of another coil of radius '$$3 R$$' carrying current $$4 A$$ is '$$B_2$$'. The ratio $$B_1:B_2$$ is

Two wires $$2 \mathrm{~mm}$$ apart supply current to a $$100 \mathrm{~V}, 1 \mathrm{~kW}$$ heater. The force per metre between the wires is ( $$\mu_0=4 \pi \times 10^{-27}$$ SI unit)