자기력 (F_{m})이 구심력 (F_{n}) 역할을 합니다.

\displaystyle qvB = \dfrac{mv^{2}}{r} \Rightarrow r = \dfrac{mv}{qB}

\displaystyle r = \dfrac{(6.64 \times 10^{-27}~\text{kg})(5.0 \times 10^{6}~\text{m/s})} {(2 \times 1.6 \times 10^{-19}~\text{C})(0.25~\text{T})}

\displaystyle r = \dfrac{3.32 \times 10^{-20}}{8.0 \times 10^{-20}} \approx 0.415~\text{m} \approx 0.42~\text{m}