A current carrying conductor experiences maximum force in magnetic field when the angle between current element and direction of magnetic field is

Two parallel conductors carry current in opposite directions as shown in the figure. One conductor carries a current of $$20 \mathrm{~A}$$. Point $$C$$ is a distance $$d / 2$$ to the right of a 20 A current. If $$d=18 \mathrm{~cm}$$ and $$i$$ is adjusted so that the magnetic field at $$C$$ is zero, the value of the current $$i$$ is

Two long parallel wires carry equal current $$i$$ flowing in the same directions are at a distance $$4 d$$ apart. The magnetic field $$B$$ at a point $$P$$ lying on the perpendicular line joining the wires and at a distance $$x$$ from the mid-point is

In a cathode ray tube, a potential difference of 3000 volts is maintained between the deflector plates whose separation is $$2 \mathrm{~cm}$$. A magnetic field of $$2.5 \times 10^{-3} \mathrm{~Wb} / \mathrm{m}^2$$ at right angles to electric field gives no deflection of the electron beam, which received an initial acceleration by a potential difference of $$10000 \mathrm{~V}$$. Calculate $$(\mathrm{e} / \mathrm{m})$$ of an electron.