Five particles are shot from the left into a region that contains a uniform electric field. The numbered lines show the paths taken by the five particles. A negatively charged particle with a charge -3Q follows path 2 while it moves through this field. Do not consider any effects due to gravity.
-In which direction does the electric field point?

Question

Five particles are shot from the left into a region that contains a uniform electric field. The numbered lines show the paths taken by the five particles. A negatively charged particle with a charge -3Q follows path 2 while it moves through this field. Do not consider any effects due to gravity. 
-In which direction does the electric field point?

Quizplus · Accepted Answer

As the negatively charged particle moves through the field along path 2, it is deflected downward. This implies that there is an upward electric force acting on the particle. By convention, the direction of the electric field is defined as the direction of the force that a positive test charge would experience in that field. Therefore, the electric field must point in the opposite direction, which is downward. This is consistent with choice D, toward the bottom of the page.

Five Particles Are Shot from the Left into a Region