A stream of protons passes a given point in space at a rate of 10 E9 protons/second. What magnetic field do they produce 2.0 m from the beam? Kind of know where to start, but not exactly. the current would be 10 E9 multiplied by 1.6 E-19 i think. and then i think i would use B=(permativity of free space x I)/(2pir) using 2.0 m as r, but i'm not sure. help?