A long, thin rod (length = 4.0 m) lies along the x axis, with its midpoint at the origin. In a vacuum, a +8.0C point charge is f
ixed to one end of the rod, and a -8.0C point charge is fixed to the other end. Everywhere in the x, y plane there is a constant external electric field (magnitude 8.0 × 10^3 N/C) that is perpendicular to the rod. With respect to the z axis, find the magnitude of the net torque applied to the rod.
Force on each of the charges of 8 C due to uniform electric field in x -y plane will be equal and opposite because one is positive charge and the other is negative charge. They will make a couple
Each of the forces of the couple will act in x - y plane and will be equal to
Gravity always works as a pair of <em>EQUAL</em> forces ... one in each direction between two masses. Your weight on the Earth is exactly the same as the Earth's weight on you.
