JEE Main 2020 — Magnetic Effects of Current Question with Solution

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