In problem 3, what is the direction of the electric field between points A and B
ID: 1489333 • Letter: I
Question
In problem 3, what is the direction of the electric field between points A and B, and how the electric potential is compared between points A and B?
(a) Electric field is directed from A to B, and electric potential VA > VB
(b) Electric field is directed from A to B, and electric potential VA < VB
(c) Electric field is directed from A to B, and electric potential VA = VB
(d) Electric field is directed from B to A, and electric potential VA > VB
(e) Electric field is directed from B to A, and electric potential VA < VB
The answer is E but I don't understand WHY. Please explain.
(problem 3: A proton (mass = kg 27 1.67 10 × , charge = 1.6 × 1019C ) moving horizontally to the right at a speed of 1.5 10 m/s 5 × enters a uniform electric field at point A (the electric field lines are not shown). It is observed that in the electric field the proton moves in a straight line but slows down and comes to a momentary rest at point B. Find the difference (absolute value) in electric potential at points A and B. Neglect gravity.
Answer to problem 3: 117.4 V)
Explanation / Answer
(e) Electric field is directed from B to A, and electric potential VA < VB
Because, we know that the direction of electric field is determined by the direction of the force it would exert on the positive charge. The electric force lines will emerge from A to point B as the charge is at left, point A (this is the entry point of the electric field for the positive charge proton). So electric field lines will originate from B to A.
Regarding potential, distances are required.