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

A constant current flows from A to B as shown in the figure. What is the direction of current in the circle?

An electron moves with speed of 2 $$\times$$ 10$$^5$$ m/s along the positive x-direction in a magnetic field $$B = (\widehat i - 4\widehat j - 3\widehat k)\,T$$. The magnitude of the force (in N) experienced by the electron is