electric physics
posted by sweety .
Near Earth, the density of protons in the solar wind (a stream of particles from the Sun) is 12.4 cm3, and their speed is 576 km/s. (a) Find the current density of these protons. (b) If Earth's magnetic field did not deflect the protons, what total current in amperes Earth receive?

change km/s to cm/s, then multiply density given times speed.
Current = current density*area crosssection earth/charge per proton 
For part (b), multiply the current density (from part a) by pi R^2, where R is the radius of the Earth.