An electric current $I$ enters and leaves a uniform circular wire of radius $r$ through diametrically opposite points. A charged particle $$q$$ moves along the axis of circular wire passes through its centre with speed $$v$$. The magnetic force on the particle when it passes through the centre has a magnitude

A regular hexagon of side $$m$$ which is a wire of length 24 m is coiled on that hexagon. If current in hexagon is $$I$$, then the magnetic moment,

Two particles of masses $$m_1=m,m_2=2m$$ and charges $$q_1=q,q_2=2q$$ entered into uniform magnetic field. Find $$F_1/F_2$$ (force ratio).

A long solenoid has 20 turns cm$$^{-1}$$. The current necessary to produce a magnetic field of 20 mT inside the solenoid is approximately