(a) A small metal sphere has a mass of 0.15 g and a charge of -23.0 nC. It is 10
ID: 2078861 • Letter: #
Question
(a) A small metal sphere has a mass of 0.15 g and a charge of -23.0 nC. It is 10.0 cm directly above an identical sphere with the same change. This lower sphere is fixed and cannot move. (i.) What is the magnitude of the force between the spheres? (ii.) If the upper sphere is released, it will begin to fall. What is the magnitude of its initial acceleration? (b) A small glass bead has been charged to +20 nC. A tiny ball bearings 1.0 cm above the bead feels a 0.018 N downward electric force. What is the charge on the ball bearing? (c) In the figure below, charge q_2 experiences no net electric force. What is q_1?Explanation / Answer
1.(i) Fe = k q1 q2 / r^2
= (9 x10^9 ) (23 x 10^-9)^2 / (0.10^2)
Fe = 4.761 x 10^-4 N upward
(ii) Fnet = Fe - m g = (4.761 x 10^-4) - (0.15 x 10^-3 x 9.81)
= - 9.954 x 10^-4 N
a = Fnet / m = 6.64 m/s^2 ......Ans
(b) Fe = k q1 q2 / r^2
0.018 = (9 x 10^9) (20 x 10^-9)(q) / (0.01^2)
q = 10 x 10^-9 C Or 10 nC
(c) force due to q1:
F1 = k q1 q2 /0.20^2
force due to -2nC:
F2= - k (2nC)(q2) / 0.10^2
Fnet -= F1 + F2 = 0
q1 / 0.20^2 = 2 / 0.10^2
q1 = 8 nC .........ANs
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