Question

a) A +100-μC charge produces 1.5 T field 2 cm from the charge. Determine the magnitude of velocity of the charge. b) What magnetic field is produced by a charge twice that in part a) 4 cm away from it?

Answer 1

Part a)

$$qvB=\dfrac1{4\pi\epsilon_0}\dfrac{q^2}{r^2},\\\space\\ v=\dfrac1{4\pi\epsilon_0}\dfrac{q}{r^2B}=1.5·10^9\text{ m/s}.$$

Part b) The field will be 4 times weaker, or 0.375 T.