5) Shown below are three fixed charges. 2m a. Find the net force on the 4C charg

Question

5) Shown below are three fixed charges. 2m a. Find the net force on the 4C charge. Show your calculations. b. Now put an imaginary box around the two charges on the left as shown. Treat these charges as one object. What is the net charge on this object? What is the force (magnitude and direction) exerted on this object by the 4uC charge? If the magnitude is zero state that explicitly, if not, explain how you determined your c. answer. d. Is your answer to part (c) consistent with Newton's Third Law? If not, resolve the inconsistency

Explanation / Answer

5)(a) The net force on 4uC chare will be calculated as follows:

F4 = kq1Q/r1^2 + kq2Q/r2^2

F2 = 9 x 10^9 x 1 x 10^-6 x 4 x 10^-6/3^2 - 9 x 10^9 x 1 x 10^-9 x 4 x 10^-6/2^2 = 0.004 N

Hence, F4 = 0.004 N = 4 x 10^-3 N

b)The net charge on the box will be:

Qnet = 1 uC + (-1 uC) = 0

Hence, Qnet = 0

c)Since the net charge on the imaginary box is zero as 1 + (-1) = 0; The electric force between the box and 4uC will be zero.

d)If the objects are considered individually then the Newton's third law is followed and if they are considered as the system of charge and the net charge on this system is zero there will be no charge on the box and hence no force and Newton's law is not applicable on this system.

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