Three point charges are arranged on a line. q3 = + 5.00 nC and is at the origin. Charge q2 = -3.00nC and is at x =4.00cm. Charge q1 is at x = 2.50 cm.
What is the sign and magnitude of q1 if the net force on q3 is zero?
Net force on q3 = force by q1 + force by q2 = 0
=> kq1q3/r12 + kq2q3/r22 = 0
=> kq3( q1/r12 + q2/r22) =0
=> q1/r12 + q2/r22 =0
=> q1/ (2.5)2 + (-3)/ (4)2 = 0
=> q1 = (3/16)*6.25
=> q1 = 1.171nC
so, Sign of q1 is Positive and magnitude = 1.171 nC