The figure shows a region of length ‘l’ with a uniform magnetic filed of 0.3T in it and a proton entering the region with velocity 4 × 105 ms-1 making an angle 600 with the field. If the proton completes 10 revolution by the time it cross the region shown, ‘l’ is close to (mass of proton = 1.67 × 10-27 kg, charge on the proton = 1.6 × 10-19C)