[" An "alpha" particle is moving along a circle of radius "R" with a constant angular velocity "omega.],[" Point "A" lies in the same plane at a distance "2R" from the centre.The point "A" records "],[" magnetic field produced by "alpha" particle.If the minimum time interval between two "],[" successive times at which "A" records zero magnetic field is "^(c)t'," the angular speed "omega," in "],[" terms of "t" is: "],[[" 1) "(2 pi)/(t)," 2) "(2 pi)/(3t)," 3) "(pi)/(3t)," 4) "(pi)/(t)]]