When introduced into a region where an electric field is present,a proton with initial velocity $\overrightarrow { \mathbf { v } }$ will eventually move
A)along an electric field line,in the positive direction of the line.
B)along an electric field line,in the negative direction of the line.
C)to a point of decreased potential.
D) as described in both (a)and (c).

Question

Quizplus · Accepted Answer

When a proton is introduced into a region where an electric field is present, it experiences an electric force, which accelerates it along the field line. The direction of force on a positive charge is the same as the direction of the electric field. Therefore, the proton will move along the electric field lines. As it moves, it gains or loses potential energy depending on the direction of the electric field lines and the charge of the proton. 
In this case, the proton has an initial velocity in the positive direction of the electric field, but it will eventually slow down and come to rest at a point of decreased potential. This can be seen from the fact that as the proton moves along the field lines, it will move from higher potential to lower potential. Therefore, the correct choice is C.

When Introduced into a Region Where an Electric Field Is v→\overrightarrow { \mathbf { v } }v

When Introduced into a Region Where an Electric Field Is $\overrightarrow { \mathbf { v } }$