1. Read each part carefully. Show all your work for each part of the question. The parts within the question may not have equal weight.
Figure 1
Scale = 1 m per box
Figure 2
Figure 1 shows a region of space with four point charges A, B, C, and D that lie in the plane of the screen. The dotted circle represents the cross-section of a spherical Gaussian surface centered on the origin. The spherical Gaussian surface has a radius r that can be varied. A graph that represents the net electric flux through the spherical Gaussian surface as a function of its radius is shown in Figure 2.
(a) State which of the charges is/are positive and which is/are negative. Justify your answer.
(b) Rank the magnitudes of the charges from highest to lowest. If any two charges have the same magnitude, explicitly state this. Justify your ranking using a physics principle or law.
Suppose that the charge C at the origin is now removed for parts (c), (d), and (e).
(c) Describe how this would change the graph shown in Figure 2. Be as specific as possible.
(d) Which of the following best describes the direction of the electric field at the origin: (+x and +y), (+x and -y), (-x and +y), or (-x and -y). Justify your answer.
(e) State whether the electric potential at the origin is positive, negative, or zero. Justify your answer.
