A proton and an electron are each placed in a uniform electric field of 2500 V m⁻¹…

Step 1. Force. $F = eE = 1.602 \times 10^{-19} \times 2500 = 4.01 \times 10^{-16}\ \text{N}$ on each.

Step 2. Electron. $a_e = \dfrac{4.01 \times 10^{-16}}{9.109 \times 10^{-31}} = 4.40 \times 10^{14}\ \text{m s}^{-2}$.

Step 3. Proton. $a_p = \dfrac{4.01 \times 10^{-16}}{1.673 \times 10^{-27}} = 2.40 \times 10^{11}\ \text{m s}^{-2}$, in the opposite direction.

Step 4. Ratio. $\dfrac{m_p}{m_e} = 1837$.