Question

Three point charges, two positive and one negative, each having a magnitude of 30 µC are placed at the vertices of an equilateral triangle (21 cm on a side). a -q +q +q What is the magnitude of the electrostatic force on one of the positive charges? The value of the Coulomb constant is 8.98755 × 109 N · m2 /C 2 . Answer in units of N.

Answer 1

Assuming the +ve is at top vertex

F = kq1q2/r^2 = 9x10^9 x 30 x 30 x 10^-12 / 0.21^2 = 183.67 N

This is force between two charges.

One force will be directed along first side (towards 3rd quadrant) and other along second side (towards 2nd quadrant)

In short they will make an angle of 120 deg between them

Hence, using resultant vector

R^2 = P^2 + Q^2 - 2PQcos@

= 183.67^2 + 183.67^2 - 2 x 183.67 ^2 x cos120

R = 318 N