A proton is released from rest inside a region of constant, uniform electric field ?1E1 pointing due north. 22.3 s22.3 s after it is released, the electric field instantaneously changes to a constant, uniform electric field ?2E2 pointing due south. 6.81 s6.81 s after the field changes, the proton has returned to its starting point.

A proton is released from rest inside a region of constant, uniform electric field ?1E1 pointing due north. 22.3 s22.3 s after it is released, the electric field instantaneously changes to a constant, uniform electric field ?2E2 pointing due south. 6.81 s6.81 s after the field changes, the proton has returned to its starting point.