A proton is moving undeflected in a region of crossed electric and magnetic fields at a constant speed of 2 × 10^5 ms^-1. When the electric field is…

A proton is moving undeflected in a region of crossed electric and magnetic fields at a constant speed of $\displaystyle 2 \times 10^5 \mathrm{~ms}^{-1}$. When the electric field is switched off, the proton moves along a circular path of radius $\displaystyle 2$ cm. The magnitude of electric field is $\displaystyle x \times 10^4 \mathrm{~N} / \mathrm{C}$. The value of $\displaystyle x$ is $\displaystyle \_\_\_\_$. Take the mass of the proton $\displaystyle =1.6 \times 10^{-27} \mathrm{~kg}$.