At point A, charge is entering in a magnetic field in which direction of field is shown in the figure. The velocity of particle is \(u\) making an angle of \(45^{\circ}\) with field. We resolve it in two directions, one along the field and other perpendicular to it. Since \(\mathrm{u} \sin 45^{\circ}\) is perpendicular to \(\mathrm{H}\), it will create a rotatory effect on the charge. So charge particle will start rotating with axis along the direction of \(\mathrm{H}\). At the same time it will move forward with velocity \(\mathrm{u}\) \(\cos 45^{\circ}\). Under both these motions, it will have helical path as shown in the figure.