Write an equation of Lorentz force $\stackrel{\rightharpoonup }{\mathrm{F}}$ acting on a charged particle having charge $\mathrm{q}$ moving in a magnetic  field $\stackrel{\rightharpoonup }{\mathrm{B}}$ with a velocity$\stackrel{\rightharpoonup }{\mathrm{v}}$ in vector form. 

Equal currents $\mathrm{I}$ and $\mathrm{I}$ are flowing through two infinitely-long parallel wires. What will be the magnetic field at a point mid-way between them, when the currents are in same direction,

Equal currents $\mathrm{I}$ and $\mathrm{I}$ are flowing through two infinitely-long parallel wires. What will be the magnetic field at a point mid-way between them, when the currents are in opposite directions ?

The paths of three particles A, B and C moving in a uniform magnetic field, denoted by crosses (x), are shown in the figure. The field is perpendicular to the plane of paper pointing downwards. State the nature of charge on each particle.