An electron is released with a velocity of 5 × 106 ms-1 in an electric field of 103 N C-1 which has been applied so as to oppose its motion. How much time could it take before it is brought to rest?

Since electric field is applied so as to oppose the motion of electron,a=−eEmretardation=−1.6×10−19×1039.1×10−31=−1.758×1014ms−2Now,   u=5×106ms−1,   v=0Using  the  relation:  v2−u2=2as,  we  gets=7.11×10−2mUsing  the   relation  :  v=u+at,  we  gett=2.844×10−8s