The figure shows a region of length ' l ' with a uniform magnetic field of 0.3 T in it and a proton entering the region with velocity 4 × 10^5 ms^-1…

The figure shows a region of length ' $\displaystyle l$ ' with a uniform magnetic field of $\displaystyle 0.3$ T in it and a proton entering the region with velocity $\displaystyle 4 \times 10^5 \mathrm{~ms}^{-1}$ making an angle $\displaystyle 60$° with the field. If the proton completes $\displaystyle 10$ revolution by the time it cross the region shown, ' $\displaystyle l$ ' is close to (mass of proton $\displaystyle =1.67 \times 10^{-27} \mathrm{~kg}$, charge of the proton $\displaystyle =1.6 \times 10^{-19} \mathrm{C}$ )