\(\overrightarrow{ B }= B \hat{ j } \text { Energy }=728\,eV\)
Energy \(=\frac{1}{2} mv ^{2}\)
\(728\,eV =\frac{1}{2} \times 9.1 \times 10^{-31} \times v ^{2}\)
\(728 \times 1.6 \times 10^{-19}=\frac{1}{2} \times 9.1 \times 10^{-31} \times v ^{2}\)
\(v =16 \times 10^{6} m / s\)
\(E=v B\)
\(E =16 \times 10^{6} \times 12 \times 10^{-3}\)
\(E =192 \times 10^{3}\,V / m\)