Question

Lab Section: 3 Due January 25, 2019 1. (18.3.25) Point charges of 5.00 puC and -3.00 uC are placed 0.250 m apart. (a) Where can a third charge be placed so that the net force on it is zeroi? (b) What if both charges are positive? 2. (18.8.51) (a) What is the electric field 5.00 m from the center of the terminal of a Van de Graaf with a 3.00 mC charge? Note that the field is equivalent to that of a point charge at the center of the terminal. (b) At this distance, what force does the field exert on a 2.00 uC charge on the Van de Graaf's belt?

Answer 1

Concept:- we use the superposition principle of field to find the point where the two fields add to zero, ***************************************************************************************************
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Concept: - we use the superposition principle of field to find the point where the two fields add to zero, force to be zero, field must be zero. Let field be zero at point P, at a distance d to the right of - 3 mu c, so, at magnitude of field due to both charges must be equal as their directions are opposite so, Vertical-bar E_1 Vertical-bar = Vertical-bar E_2 Vertical-bar at p or, 5 mu c/4 pi epsilon_0 (d + 0.25 m)^2 = 1 - 3 mu c/4 pi epsilon_0 d^2 or, 5/(d + 0.25)^2 = 3/d^2 or, d = 0.86 m to the right of - 3 mu c if both are positive, field will be zero between the charges, let it be zero at p, point at a distance d to the right of 5 mu c, so, Vertical-bar E_1 Vertical-bar = Vertical-bar E_2 Vertical-bar at P or, Vertical-bar 5 mu c Vertical-bar /4 pi epsilon_0 d^2 = Vertical-bar 3 mu c Vertical-bar /4 pi epsilon_0 (0.25 - d)^2 or, 5/d^2 = 3/(0.25 - d)^2 or, d = 0.14 m to the right of 5 mu c