Question

Dr Alexander gave you the electric field line picture shown as part of your lab assignment. Unfortunately, she had a bad day, and when she copied the picture, there were some circular blobs on the scanner, which covered up important parts of the drawing 1. There is a single point charge inside the small circle. Is that charge positive or negative? How do you know? (A "single point charge" means all the charge is located at a single point, not that the charge has a value of one.) a. b. Assume there is at most one point charge inside the bigger circle. Fill in the missing parts of the picture by drawing the location and sign of the point charge inside the large circle, and if necessary, extend the field lines Which charge is larger, the one inside the small circle or the one inside the big circle? Justify your answer. c.

Answer 1

(a) small circle has negatively changed as the lines of force going inside (b) (c) The charge inside big circle is larger as the number of field lines coming out from this are more. 2 phi_A = 3q + q/epsilon_0 = 4q/epsilon_0 phi_B = -3q - q/epsilon_0 = -4q/epsilon_0 phi_C = -q + q/epsilon_0 = 0 phi_D = 3q + q - q/epsilon_0 = 3q/epsilon_0 phi_E = + 3q + q - q - 3q/epsilon_0 = 0 so, phi_E = phi_E < phi_D < phi_A = phi_B