Question

charges +2q,+q,+q are placed at the corners of an equilateral triangle.if E is the electric field at the centre of the triangle due to the charge +q, then magnitude of the resultant electric field at the centre is

Answer 1

The resultant of +q and +q is
$R= \sqrt{E^2+E^2-2E^2cos60}=\sqrt{E^2+E^2-E^2}=E$
the that resultant acts parallel to electric field due to +2q but opposite in direction
So final resultant is E acting away from the charge +2q